Method for producing iron carbide

ABSTRACT

An apparatus and method of producing iron carbide of predetermined quality is disclosed. The method of producing iron carbide (Fe 3  C) comprises reducing and carburizing an iron-containing raw material containing iron oxides (e.g., hematite) or iron hydroxides as main components, wherein the raw material is partially reduced to a reduction ratio of 50 to 65% by a gas containing mainly hydrogen in a first stage of the reaction process, then the partially reduced raw material is further reduced and carburized with a gas containing mainly hydrogen and methane in a second stage of the reaction process to provide iron carbide.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producing asuitable raw material for iron making and steel making. Moreparticularly, the present invention relates to a method and apparatusfor producing a material comprising iron carbide (Fe₃ C) as the maincomponent, wherein the material is used in an electric furnace and thelike for steel making.

BACKGROUND OF THE INVENTION

The production of steel normally comprises the steps of converting ironore to pig iron using a blast furnace, and thereafter converting the pigiron into steel using an open hearth furnace or a converter. Such atraditional method requires large amounts of energy and large-scaleequipment, and has a high cost. Therefore, for a small-scalesteel-making operation, a method comprising the steps of directlyconverting iron ore into raw materials used in the steel-making furnace,and converting the raw material into steel using an electric furnace andthe like has been used. With respect to direct iron making, a directreduction process has been used to convert iron ore into reduced iron.

However, the reduced iron produced by a direct reduction process ishighly reactive and reacts with oxygen in the air to generate heat.Therefore, it is necessary to seal the reduced iron with an inert gas,or by some other measure, during transportation and storage of thereduced iron. Accordingly, iron carbide (Fe₃ C) containing acomparatively high iron (Fe) content, and which has a low reactionactivity and can be easily transported and stored, has recently beenused as the iron-containing material for steel making in an electric arcfurnace and the like.

Furthermore, an iron-making or steel-making material containing ironcarbide as the main component is not only easy to transport and store,but also has the advantage that the carbon combined with iron can beused as a source of fuel in an iron-making or steel-making furnace, andcan be used as a source to generate microbubbles which accelerate thereaction in the steel-making furnace. Therefore, materials for ironmaking or steel making containing iron carbide as the main componentrecently have attracted special interest, as set forth in publications1, 2, and 3 listed hereafter.

According to one method of producing iron carbide, iron oxides (e.g.,hematite (Fe₂ O₃), magnetite (Fe₃ O₄), wustite (FeO), etc.) in iron oreare reduced and carburized in a single process. A "single process" meansan operation performed by simultaneously introducing a reducing gas anda carburizing gas to a single reactor, as shown in the followingreaction formulas (1)-(6). Fine-sized iron ore is charged into afluidized bed reactor and is reacted with a gas mixture comprising areducing gas (e.g., hydrogen gas) and a carburizing gas (e.g., methanegas and the like) at a predetermined temperature.

    3Fe.sub.2 O.sub.3 +H.sub.2 →2Fe.sub.3 O.sub.4 +H.sub.2 O(1)

    Fe.sub.3 O.sub.4 +H.sub.2 →3FeO+H.sub.2 O           (2)

    FeO+H.sub.2 →Fe+H.sub.2 O                           (3)

    3Fe+CH.sub.4 →Fe.sub.3 C+2H.sub.2                   ( 4)

    Fe.sub.3 O.sub.4 +CH.sub.4 +2H.sub.2 →Fe.sub.3 C+4H.sub.2 O(5)

    3FeO+CH.sub.4 +H.sub.2 →Fe.sub.3 C+3H.sub.2 O       (6)

The overall reaction of equations (1) through (4) and (5) and (6) is setforth in reaction formula (7):

    3Fe.sub.2 O.sub.3 +5H.sub.2 +2CH.sub.4 →2Fe.sub.3 C+9H.sub.2 O.(7)

Further, prior art in the field of the present invention is described,for example, in the publication of the Japanese translation ofInternational Patent Application No. 6-501983 (PCT/US91/05198),including the operation report of industrial equipment in publication 11listed hereafter, and those described in publications 4, 5, and 8 listedhereafter. In addition, German Patent No. 4320359 discloses a processprovided with two-stage reactors.

The carburization process also can be accomplished by using carbonmonoxide (CO) as the carburizing gas component as set forth in thefollowing reaction formula (8).

    3Fe+CO+H.sub.2 =Fe.sub.3 C+H.sub.2 O                       (8)

Prior art in the above-described field further is described inpublications 6 and 7 listed hereafter.

                  TABLE 9                                                         ______________________________________                                        Publications                                                                  ______________________________________                                        1     "TEKKO KAI," July, 1993, pp. 40-44.                                           "Iron Carbide, iron source attracting interest"                         2     "The potential for use of iron carbide as an electric                         furnace raw material," 16th Advanced Technology Sympo-                        sium ISS-AIME Alternate Iron Sources for Electric Arc                         Furnace, May 2-5, 1993, Myrtle Beach.                                   3     A. W. Swanson, "Iron Carbide, a possible replacement for                      premium quality scrap," Preprint 93-28, presentation at                       the SME Annual Meeting, Reno, Nevada, February 15-18,                         1993.                                                                   4     F. V. Povoa, "Role of iron are supplier in scrap substi-                      tute process development," Iron & Steel Scrap, Scrap                          substitutes direct steel-making, March 21-23, 1995,                           Atlanta, Georgia.                                                       5     Nakagawa et al., "Influence of the nature of iron ore                         on the formation of cementite," CAMP-ISU Vol. 7 (1994)-                       85.                                                                     6     Hayashi et al., "Formation of iron carbide from iron                          ore using fluidized bed (Production of iron carbide-2)                        CAMP-ISU Vol. 8 (1995)-111.                                             7     Hayashi et al., "Formation of iron carbide from iron                          ore (production of iron carbide-1), CAMP-ISU Vol. 8                           (1995)-110.                                                             8     Nakagawa et al., "Influence of gas composition and                            temperature on formation of cementite," CAMP-ISU Vol. 8                       (1995)-109.                                                             9     Mori et al., "New iron making process and fluidized                           bed," Chemical Equipment, June, 1986, pp. 99-108.                       10    T. P. McAloon, I&SM, February, 1994.                                    11    33 Metal Producing, January, 1995 (pp. 36, 37 & 49).                    ______________________________________                                    

The above-described conventional methods have the followingdisadvantages.

Regarding conventional methods described in the publication of theJapanese translation of International Patent Application No. 6-501983(PCT/US91/05198), and publications 3 and 5, which use present-dayindustrial equipment, the iron-containing material for iron makingcontains at least one, or a mixture of two or more, iron oxides, such ashematite, magnetite, and wustite, and iron hydroxides, such as ferroushydroxide and ferric hydroxide, as the main component, e.g., iron ore ordust and the like generated from iron-making processes. The process ofremoving oxygen combined with iron atoms of the iron-containing materialfor iron making uses methane (CH₄) as a component in a carburizingreaction gas to convert the iron-containing material into iron carbide(also termed cementite and Fe₃ C herein) in a single reactor at atemperature of about 600° C. using a gas mixture containing methane. Thegas mixture is suitable for the carburizing reaction, that is, the mainreaction (i.e., reduction and carburization) is performed in a singleprocess. Because methane (CH₄) in this process is used directly as thecarburizing gas, the carbon atom in methane acts as the carburizingcomponent and the hydrogen atoms in methane act as the reducingcomponent. This process has the advantages that the amount of H₂(hydrogen gas) and CO (carbon monoxide) consumed is small and theapparatus is simple. However, the following disadvantages also areapparent.

Because the reaction is a catalytic reaction between a solid iron oxideand reducing and carburizing gases, the reaction speed is slow and thereaction time (i.e., a time required for a complete conversion to thedesired iron carbide product) is long, thereby requiring a long time toobtain a predetermined amount of the steel-making material compared to aconventional iron-making method, such as a blast furnace process and thelike. Therefore, it is necessary to enlarge the scale of the equipmentin order to increase production per unit time. As a result, the mainobjectives of the direct iron-making method, which are to decreaseequipment scale and production costs compared to traditional iron-makingmethods, are not met.

The reaction temperature preferably is increased in order to increasereaction speed. However, in a reducing reaction of iron oxide, when thereaction temperature is increased to about 600° to 700° C., even thoughthis temperature is below the melting point of iron oxide, the angularsurface of an iron oxide crystal becomes smooth due to surface tension(referred to as sintering or semi-melting, hereafter termed "sintering")as the reduction ratio approaches 100%. This phenomena results in a lossof reaction activity. As illustrated in FIG. 8, and in publication 9, agraph of the relationship between reaction temperature and reaction timein the reducing reaction of hematite shows that the reaction timeincreases in the range of about 600° to 700° C. when about 100%reduction is approached.

Therefore, the objective of increasing reaction speed is not achieved,even if the reaction temperature is increased. When a large amount ofwater is generated in the reducing reaction, or when the raw materialdoes not flow smoothly due to a structural feature of the reactor, thewater reacts with the iron ore to cause local solidification, that is, aso-called "sticking phenomenon" occurs. When sintering or stickingoccurs, the iron oxide particles condense or agglomerate and, therefore,become impossible to remove mechanically.

Furthermore, the reducing reaction shown in above reaction formulas (1)through (3), and the carburizing reaction shown in above reactionformula (4), are performed in a single process by contacting iron oxidewith a gas mixture containing hydrogen, methane, and the like.Therefore, both the reducing and carburizing reactions must beconsidered, and the composition of the reaction gas and the reactiontemperature cannot be independently set to optimize the reducing andcarburizing reactions, respectively.

Therefore, the amount of reaction gas (i.e., the amount of a reactiongas to be contacted in order to produce a unit amount of product) isincreased. As shown in Table 8a described hereafter, the amounts ofenergy, electrical power, cooling water, and the like consumed in aconventional iron carbide producing process described in the publicationof the Japanese translation of International Patent Application No.6-501983 (PCT/US91/05198) are greater than the corresponding amountsused in a conventional direct reduction iron-making process (e.g., theMIDREX process, etc.).

The method described in German Patent No. 4320359 which reduces theamount of the reaction gas, completes the reaction in two stages. In thefirst stage, iron ore is partially reduced using a mixture of a 50 to20% equivalent amount of a circulating reaction gas, and a 50 to 80%equivalent amount of a remaining, partially reacted, circulatingreaction gas discharged from the second stage. Then, the partiallyreduced iron ore is transferred to the second stage, and a furtherreduction and carburization is conducted using 50 to 80% equivalentamount of the circulating reaction gas. An object of the describedmethod is to enhance the reaction efficiency of the gas by bringing 50to 80% of the circulating reaction gas into contact with the ore in twostages. The described method has accomplished some reduction in theconsumption of reaction gas compared to the conventional methoddescribed in the publication of the Japanese translation ofInternational Patent Application No. 6-501983 (PCT/US91/05198), orpublication 11, which describes present-day industrial equipment.

However, the following disadvantages can be considered. In particular,the circulating reaction gas introduced into the second stage requires asufficient carbon potential (i.e., chemical reaction force) to produceiron carbide. Therefore, it is necessary to increase the methaneconcentration of the reaction gas. Accordingly, the concentration ofhydrogen gas as the reducing component in the reduction gas isrelatively low. Also, because the gas after the completion of thereaction in the second stage contains a high water and carbon dioxidecontent as products of the reducing reaction, the reduction capabilityof the gas is lowered. Therefore, the reaction time in the first stageis increased. Accordingly, a reduction in the total reaction time forthe first and second stages cannot be achieved.

The gas composition and temperature of the first and second stagescannot be independently set, and, therefore, the reduction ratio or themetallization ratio, and the carburization ratio cannot be independentlycontrolled.

The processes disclosed in publications 6 and 7 use carbon monoxide (CO)gas as the carburizing reaction gas component as described above, and aconsiderable reduction in reaction time of the carburizing reaction isreported. However, a comparison between the overall reaction formula tofully convert hematite into iron carbide when using carbon monoxide (CO)or methane (CH₄), respectively, as the carburizing gas, must beconsidered.

In case of CO, the overall reaction formula is as follows:

    3Fe.sub.2 O.sub.3 +2CO+11(H.sub.2 and/or CO)=2Fe.sub.3 C+11(H.sub.2 O and/or CO).                                               (9)

In case of CH₄, the reaction formula is as follows:

    3Fe.sub.2 O.sub.3 +2CH.sub.4 +5(H.sub.2 and/or CO)=2Fe.sub.3 C+9(H.sub.2 O and/or CO.sub.2).                                         (10)

As readily illustrated in reaction formulas (9) and (10), when carbonmonoxide is used as the carburizing reaction gas component, it isnecessary to supply 2.6 times ((2+11)/5) the amount of a gas mixture ofCO and H₂ compared to using methane. H₂ and CO are produced industriallyby bringing a natural gas containing methane (CH₄) as a main componentinto contact with steam in the presence of a catalyst at a hightemperature and under high pressure, followed by catalytic reaction(referred to as steam gas reforming process). Accordingly, when carbonmonoxide is used as the carburizing gas, an expensive steam gasreforming unit is further required and energy consumption increases.This relationship is shown in FIG. 10.

The present invention solves the above-described disadvantages of theconventional method of producing Fe₃ C. A main objective of the presentinvention is to provide a method and apparatus for producing ironcarbide efficiently and economically. The method and apparatus arecapable of shortening the reaction time, reducing consumption ofreaction gas and energy, and enabling use of smaller size equipment.

These objects, as well as other objects and advantages of the presentinvention, will become apparent to those skilled in the art from thefollowing description with reference to the accompanying drawings.

SUMMARY OF THE INVENTION

In order to accomplish the objectives of shortening reaction time,reducing consumption of reaction gas, and enabling use of smaller sizedequipment and a compact steam gas reforming unit, a method for producingiron carbide comprises reducing and carburizing iron ore containinghematite as the main component, wherein said method is characterized bypartially reducing said hematite in a first stage of a reaction process,and, subsequently, further reducing and carburizing the partiallyreduced hematite in a second stage of the reaction process.

Preferably, the first stage of the reaction process is performed using areducing gas containing mainly hydrogen and the second stage of thereaction process is performed using a reducing and carburizing gascontaining mainly hydrogen and methane.

Another aspect of the present invention is to provide a method ofproducing a raw material containing iron carbide as the main componentfor iron making or steel making. The method comprises reducing andcarburizing an iron-containing raw material for iron making, such asiron ore, or dust and the like generated from an iron-making process,which contains at least one or a mixture of two or more iron oxides,such as hematite, magnetite, and wustite, and iron hydroxides, such asferrous hydroxide and ferric hydroxide, as a main component. Preferably,the partial reduction of the iron-containing raw material for ironmaking is performed by a reducing gas containing mainly hydrogen in afirst stage of the reaction process in order to provide a metallic ironcontent in a range of 25 to 75 atom % of the total iron content, and,thereafter, further reduction and carburization is performed by areducing and carburizing gas containing mainly hydrogen and methane in asecond stage of the reaction process, in order to achieve an eventualconversion ratio into iron carbide of more than 75 atom % of total ironcontent.

More preferably, the degree of partial reduction to metallic iron in thefirst stage of the reaction process is in the range of 30 to 65 atom %of total iron content for feeding to the second stage of the reactionprocess. Furthermore, the final conversion ratio into iron carbidepreferably is not less than 85 atom % of total iron content.

In the first stage of the reaction process, it is preferred to use areaction gas having a composition that does not allow formation of ironcarbide, that is suitable for reduction, and that can be producedindustrially and used in a circulating manner. Such a gas contains:

    H.sub.2 +H.sub.2 O≧40%, CO+CO.sub.2 ≦10%, CH.sub.4 ≦30%, H.sub.2 O+CO.sub.2 ≦10%.

Because increasing the amount of an inert gas, such as N₂, decreases therelative concentration of active reaction gas components, it ispreferable that the amount of inert gas is as low as economicallypossible, particularly from the point of the energy efficiency andreaction time.

In the second stage of the reaction process, a further reduction andcarburization are performed, and a raw material for iron making andsteel making having the desired degree of carburization is obtained. Itis preferred to use a reaction gas having a composition that permits thereducing and carburizing reactions to proceed simultaneously, that canbe used in a circulating manner, and that provides a sufficient reactionspeed. Such a gas contains:

    H.sub.2 +CH.sub.2 ≧65%(CH.sub.4 ≧20%),

    15%≧CO+CO.sub.2 ≧0.5%, H.sub.2 O≦1.5%.

Since H₂ O exerts an overall negative influence on the speed of thecarburizing reaction, and an increase in the amount of an inert gas suchas N₂, decreases the relative concentration of active reaction gascomponents, it is preferred that the amounts of H₂ O and inert gases arekept low, particularly from the point of the energy efficiency andreaction time.

It also is preferred to add methane to the reducing gas used in thefirst stage of the reaction process such that the hydrogen content inthe reduction gas can be adjusted, and to add hydrogen or methane to thereducing and carburizing gas used in the second stage of the reactionprocess such that the hydrogen and methane content in the reducing andcarburizing gas can be adjusted.

Furthermore, the reduction degree of hematite as the iron-containing rawmaterial for iron making in the first stage of the reaction processpreferably is in the range of 50 to 65%, more preferably 55 to 62%. Theterm "reduction degree" as used herein means a ratio of the number ofoxygen atoms eliminated to the number of oxygen atoms per iron atom ofhematite (Fe₂ O₃) (i.e., the number obtained by subtracting the numberof oxygen atoms per iron atom of the iron oxide in which the reductionreaction has proceeded from the number of oxygen atoms of hematite). Forexample, the reduction degree of magnetite (Fe₃ O₄), wustite (FeO), andreduced iron (Fe) is about 11%, about 33%, and about 100%, respectively.

The stoichiometric relationship wherein methane (CH₄) is used as areaction gas component for further reducing and carburizing reactions inthe second stage of the reaction process is as shown in formula (11):

    3FeO.sub.2/3 +CH.sub.4 =Fe.sub.3 C+2H.sub.2 O              (11)

With respect to the actual composition of FeO_(2/3), the relationshipbetween metallic iron (M Fe) and iron oxide (magnetite (Fe₃ O₄) and/orwustite (FeO)), and, further, reduction degree, when hematite (Fe₂ O₃)is used as the starting material, is summarized in Table 5. Thereduction degree is about 56%.

Preferably, the final conversion ratio of hematite into iron carbide isin the range of 90 to 99%, more preferably 93% or more, and mostpreferably 95% or more.

The reaction temperature of the first stage in the reaction processpreferably is in the range of 550° to 750° C., and more preferably 610°to 650°.

The second stage of the reaction process preferably is performed at atemperature of 550° to 750° C. in order to control the final form (e.g.,magnetite, wustite, etc.) of the residual iron oxide in a material foriron making and steel making. In order to provide magnetite as theresidual form of iron oxide, which is the most stable form, thetemperature preferably is in the range of 550° to 590° C. In order toshorten the reaction time and to perform a stable method, thetemperature preferably is in the range of 6100° to 650° C.

The reaction temperature of the second stage of the reaction processpreferably is in the range of 590° to 750° C., and more preferably 610°to 650° C.

Water vapor preferably is eliminated from the reaction gas used in thesecond stage of reaction process to decrease the partial pressure of H₂O.

Carbon dioxide and hydrogen preferably are added to the reaction gasused in the second stage of the reaction process.

The reaction pressure of the first stage and the second stage of thereaction process preferably are in the range of 1 to 9.9 kgf/cm² G ("G"is defined as gauge pressure), and more preferably 2 to 5 kgf/cm² G.

The raw material supplied to the reactors of the first stage and thesecond stage of the reaction process preferably are preheated orprecooled to a temperature in the range of ±100° C. of the reactiontemperature of the respective stage of the reaction process.

An apparatus for performing a process of the present invention producesraw materials for iron making and steel making. The raw materialscontain iron carbide as the main component. The apparatus reduces andcarburizes an iron-containing raw material for iron making (e.g., ironore or a dust and the like generated from an iron-making process whichcontain at least one or a mixture of two or more iron oxides, such ashematite, magnetite, and wustite, and iron hydroxides, such as ferroushydroxide and ferric hydroxide, as the main component).

The apparatus comprises a first-stage reaction unit for a first-stagereaction process to perform a partial reduction of the iron-containingraw material for iron making, and a second-stage reaction unit for asecond-stage reaction process to perform a further reduction and acarburization of the partially reduced iron-containing raw material,

wherein a feeding route for the raw material is connected to an upperportion of the first-stage reaction unit, and a feeding route for thepartially reduced material exiting a lower portion of the first-stagereaction unit is connected to an upper portion of the second-stagereaction unit, and a recovery route for iron carbide is operativelyconnected to a lower portion of the second-stage reaction unit,

and wherein a circulating loop for a first-stage reaction gas comprisesa first-stage reaction gas feed route having one end connected to a gasinlet thereof via a compressor and a heater, and a circulating routeexiting a gas outlet of the first-stage reaction unit connected to asecond end of the gas feed route via a scrubber, and a circulating loopof the second stage reaction gas comprising a second-stage reaction gasfeed route having one end connected to a gas inlet thereof via acompressor and a heater, and a circulating route exiting a gas outlet ofthe second-stage reaction unit connected to a second end of the gas feedroute via a scrubber,

wherein a supply route for a reducing gas containing mainly hydrogen isconnected to the first-stage reaction gas feed route and a supply routefor a reducing and carburizing gas containing mainly methane isconnected to a second stage reaction gas feed route,

thus allowing a continuous supply of the respective reaction gases toeach of the first-stage reaction unit and the second-stage reactionunit.

The apparatus permits an efficient control of the respective reactionsin the first stage and second stage of the reaction process inaccordance with the reaction processes and conditions described above.Furthermore, essentially all of the respective reaction gases can beused in a circulating manner, and the respective reaction gases can beefficiently used, in a circulating manner, after removing dusts andwater. Preferably, the apparatus of the present invention is constructedas illustrated in FIG. 5, for example, an independent gas loop for thepurpose of adjusting the composition of the reaction gas in each stageof the reaction is connected to each reaction apparatus and respectivegas-circulating loop.

The first-stage and second-stage of the reaction process preferably areperformed using fluidized bed reactors. Preferably, the fluidized bedreactor has partition walls for preventing a direct movement of rawmaterial particles from the inlet to the outlet of the reactor.

The first stage and second stage of the reaction process for preparingan iron-containing raw material for iron making which contains mainlycoarse particles, preferably is prepared in a rectangular verticalmoving bed reactor provided with multi-layer inlet and outlet wind boxeslocated at corresponding heights along opposite rectangular walls, suchthat a gas flows horizontally through the reactor, and charged solidmaterial flows vertically, e.g., the furnace illustrated in FIG. 21.

The present method of producing iron carbide and an apparatus having theabove construction demonstrate the following advantages:

1. According to the present method of producing iron carbide, thereaction process is divided into a first stage for partially reducinghematite, and a second stage for further reducing and for carburizingthe metallic iron in the iron-containing raw materials for iron making.Therefore, the gas used in the first stage of the reaction process canbe a composition which is optimized for the reducing reaction, and thegas used in the second stage of the reaction process can be acomposition which is optimized for the further reducing and thecarburizing reactions. In accordance with the present invention, thereaction speed can be increased compared to a process for producing ironcarbide wherein the reduction and carburization of hematite (i.e.,conversion to iron carbide) is performed in a single process using amixed gas of the reducing and carburizing gases. Accordingly, thereaction time (i.e., a time required for converting the iron content inhematite into iron carbide to the desired conversion ratio) can beshortened.

When the reduction degree is high, the reduction of hematite causessintering at a reaction temperature in the range of about 600° to 700°C., which in turn increases reaction time. In conventional processes,sintering is prevented by adjusting the reaction temperature to about590° C. To the contrary, in the present process of producing ironcarbide, the reducing reaction is divided into a first stage and asecond stage, and the partial reduction in the first stage of thereaction process can be adjusted to the degree where no sinteringoccurs. Therefore, it is possible to perform the reducing reaction atthe above-mentioned reaction temperature. Accordingly, it is possible toperform the reaction at a temperature higher than that of a conventionalprocess, and, accordingly, the reaction speed is further increased toshorten the reaction time.

Furthermore, the flow rate of the reducing and carburizing gasesrequired in the first stage and second stage of the reaction process canbe substantially decreased due to the above-described features of highertemperature and shorter reaction time, etc.

Since the present reaction process is divided into two stages forproducing iron carbide, two gas systems are required. This makes thesystem complex, but the productivity of a reactor of the same size isincreased by the above-mentioned shortening of the reaction time. On theother hand, a smaller reactor can be used if an increase in productionis not desired.

The degree of progress of the reducing reaction i.e., reduction ratio,can be determined by measuring the amount of steam generated in thefirst stage of the reaction process. Therefore, control of theconversion ratio to iron carbide is facilitated, even if the reactiontime varies because of a variation in quality of hematite.

It also is possible to utilize the following variations andmodifications which cannot be employed in a conventional process forproducing iron carbide using a single process, as disclosed in thepublication of the Japanese translation of International PatentApplication No. 6-501983 (PCT/US91/05198). Therefore, the presentprocess is flexible.

a. The carburizing gas has a tendency to pyrolytically decompose togenerate free carbon. To prevent decomposition, the steam in thereaction gas can be maintained at over a minimum constant concentration.Such a process step can be used only with respect to the gas used in thesecond stage of the reaction process.

b. In order to decrease the concentration of CO and CO₂, which can causethe generation of free carbon, it is useful, for example, to remove themfrom the gas by a CO₂ scrubber. The present method makes it possible toprevent the generation of free carbon, and to increase the concentrationof hydrogen gas, by subjecting CO and CO₂, which accumulate toward achemical equilibrium composition in the reaction gas of the first stageof the reaction process, to the above scrubbing operation.

c. When the conversion ratio of iron carbide becomes too high, and theFe content becomes scarce, the methane gas can be decomposed into carbonand hydrogen. Control of the conversion ratio can be performed only inthe second stage of the reaction process.

2. According to the present method of producing iron carbide, the firststage of the reaction process is performed using a reducing gascontaining mainly hydrogen, and the second stage of the reaction processis performed using a reducing and carburizing gas containing mainlyhydrogen and methane. Therefore, a partial reduction is achieved in thefirst stage of the reaction process, and a further reducing reaction anda carburizing reaction are achieved in the second stage of the reactionprocess, and the above advantage (1) can be realized.

Furthermore, the following advantages can be attained, which cannot beattained using the conventional process for producing iron carbidedisclosed in German Patent No. 4320359.

a. With respect to the first stage of the reaction process having anindependent circulating gas loop of a reaction gas, it is possible touse a gas containing a high hydrogen content (i.e., suitable forreduction), and having high reducing capability because of a low waterand carbon dioxide content. Therefore, the reaction time issubstantially shortened. In contrast, in the conventional process, theconcentration of the gas component which is essential for thecarburizing reaction (i.e., methane) is high and the concentration ofhydrogen is relatively low, and, in addition, the gas contains watergenerated by the reducing reaction in the second stage of the reactionprocess retained in the gas component. Therefore, the reaction time ofthe first stage comes long.

b. Because the reaction gas for the first stage of the reaction processis a reducing gas, essentially no iron carbide is generated in the firststage of the reaction process. Therefore, the reduction degree, or themetallization degree, can be controlled such that the reduction ratio isoptimized for rapidly achieving the desired carburization ratio in thecarburizing reaction of the second stage of the reaction process.

On the other hand, because the conventional process uses a gas having acomposition basically for the carburizing reaction, it is difficult toindependently control the reduction, or metallization, degree, and thecarburization ratio, in the first stage of the reaction process.

c. Since the first stage and second stage of the reaction process,respectively, have independent circulating loops of a reaction gas, itis possible to provide a gas composition which is optimized for therespective stages, and to independently react at an optimizedtemperature for each respective stage.

On the other hand, because a single circulating gas is used in theconventional process, independently controlling the temperature of thefirst and second stages is limited.

In comparison to a conventional process for producing iron carbide whichuses CO gas as a carburizing gas component, as disclosed in publications6 and 7, the carburizing and reducing reactions in the second stage ofthe reaction process are performed using methane, which is the maincomponent of natural gas. Methane is the main reaction gas component inthe present invention. Therefore, the apparatus for methane-reforming toCO+H₂ by steam can be made small to a scale of 1/2.6, thereby reducingenergy consumption and downsizing the equipment.

3. According to the present method of producing iron carbide, aniron-containing raw material for iron making other than iron orecontaining hematite as the main component, such as dust and sludgegenerated from iron works which comprises iron oxides (e.g., magnetite,etc.), compounds thereof with water, and one or more iron hydroxides,wherein the amount of metallic iron atoms is not more than 50 atom % oftotal iron atoms, that is, the amount of iron content as iron oxide oriron hydroxide is at least 50 atom % can be effectively processed. Theadvantages are achieved because the first stage of the reaction processis performed under optimum operating conditions (e.g., temperature,pressure, gas composition, etc.) corresponding to the specific mixtureof iron compounds in the iron-containing raw material for iron making,thereby reducing the influence of the identity of an iron compound asstarting material, and supplying to the second stage of the reactionprocess a partially reduced iron compound having the optimum reductionratio and metallic iron atom ratio. Therefore, the advantages describedabove (1) and (2) can be obtained, independent of the identity of theiron compound as the starting material. In addition, disadvantages ofthe conventional process can be overcome by shortening the reactiontime, decreasing energy consumption, and enabling the use of compactapparatus.

If the iron-containing raw materials contain metallic iron atoms in anamount of 50 atom % or more of the total iron content, it is moreeffective to directly perform the second stage of the reaction processwithout performing the first stage of the reaction process, because themetallic iron content of the raw material already is in the desiredrange.

In the first stage of the reaction process, the iron-containing rawmaterial for iron making, containing various iron oxides, ironhydroxides, or a mixture thereof as the main component, is reduced toadjust the metallic iron content within the range of 25 to 70 atom % ofthe total iron content, and then further reducing and carburizingreactions are performed by a reaction gas containing methane as the maincomponent in the second stage of the reaction process. Because theamount of hydrogen gas generated from methane in the carburizingreaction of the second stage can be essentially identical to the amountof hydrogen gas consumed in the reducing reaction of the second stage,it is possible to have the further reduction and the carburizationreactions in the second stage proceed by supplying methane as the maincomponent of the reaction gas. This result is due to a chemical reactionbalance, and is not influenced by the identity and proportion of theiron oxide in the iron-containing raw materials. Therefore, the supplyof hydrogen and carbon monoxide used in the conversion can be limited tosmall amounts, making it possible to use a small apparatus for gasreformation using steam.

The present invention, therefore, relates to a process of directly usingmethane as a main reaction component in the carburizing reaction inorder to decrease the amount of methane in the natural gas that isreformed into hydrogen and carbon monoxide, as described above.

When using hematite as the starting material, the reaction convertingiron oxide into iron carbide (Fe₃ C) using methane can be classifiedinto three reaction forms shown in FIG. 12. These reactions have beenstudied from a viewpoint of reaction kinetics. As a result, the datasummarized in FIG. 13 was obtained.

1. The reaction speed from metallic iron to Fe₃ C is the fastest.Considering only the carburizing reaction, the advantage of a processwhich reduces iron oxides or iron hydroxides, or a mixture thereof, to ametallic iron, followed by conversion into iron carbide (Fe₃ C), isshown.

2. On the other hand, when iron oxides are converted into iron carbideusing methane, the hydrogen atoms in methane (CH₄) also take part in thereducing reaction, as shown in the above formula (11) and FIG. 10,thereby making it possible to decrease the feed of hydrogen and/orcarbon monoxide through gas reformation. It is important to consider theeffects of the above items (1 and 2), and a correlation between themetallization degree in the first stage of the reaction process, and thetime of overall reaction process (i.e., total of the first-stage andsecond-stage reaction process time) is shown in FIG. 14. When theproportion of metallic iron is in the range of 25 to 70 atom %, theoverall reaction process time can be shortened. When the proportion isin the range of 30 to 65 atom %, the shortest overall reaction processtime can be realized.

According to the present invention, the final conversion ratio from theiron-containing raw material for iron making to iron carbide is 75 atom% or more. The required optimum conversion ratio of the material foriron making and steel making into iron carbide varies depending on theprocess (e.g., iron making, steel making, etc.), and purpose of saidprocess, and the present invention can meet any requirements. Forexample, when the main objective is to provide a material for an ironsource, as well as for an energy source in a steel-making furnace, and alow energy consumption is required, high conversion ratio to Fe₃ C of90% or more is preferable. On the other hand, the accelerating effect ofthe refining reaction sometimes is mainly expected by a stirring effectattributed to bubbles generated by the reaction shown in the followingformula (12), even if the energy consumption increases to some extent:

    Fe.sub.3 O.sub.4 +4Fe.sub.3 C=15Fe+4CO                     (12)

In this case, an Fe₃ C product having conversion ratio of about 75 atom% can be used. That is, the optimum conversion ratio to Fe₃ C meetingwith the respective requirement for the use of the materials for ironmaking and steel making can be achieved.

4. According to the present method of producing iron carbide, the firststage of the reaction process is a process of partially reducing theiron-containing raw materials for iron making to adjust the metalliciron content in the range of 25 to 70 atom %, i.e., the reducingreaction of the iron oxide is the main reaction. The reducing gas foriron oxide contains hydrogen (H₂) and carbon monoxide (CO). The greaterthe concentration of (H₂ +CO) and the lower the concentration of (CO₂+H₂ O) as reduction products, the greater the reaction speed.

The reducing reaction speed using H₂ is greater than using CO at thepresent reaction temperature ranges, and a shortened reaction time and adecrease in consumption of reaction gas can be accomplished.Furthermore, the reaction product of hydrogen is steam (H₂ O) which canbe removed by simply cooling the exhaust gas during treatment.Accordingly, when using hydrogen as the main component, a reaction gascan be used easily, in a circulating manner, without accumulating H₂ O,or increasing H₂ O concentration.

The above composition can be used as the gas for conducting the firststage of the reaction process. That is, the reaction for producing ironcarbide represented by the formula (4) can be suppressed by maintaininga low methane concentration. Therefore, no iron carbide is produced, andthe reducing reaction can be efficiently performed. As a result, it ispossible to provide an apparatus which can be used practically inindustry.

5. According to the present method of producing iron carbide, theremaining reducing and carburizing reactions of the iron-bearing rawmaterial for iron making, which was partially reduced and metallized inthe first phase, are performed using hydrogen and methane as the maingas components, and restricting the concentration of other components,thereby shortening the reaction time and decreasing consumption of thereaction gas.

A sufficient carbon potential (i.e., chemical reaction force) isrequired to produce iron carbide (Fe₃ C). In the case of a carburizingreaction using methane, as is apparent from formula (4), the reaction isin proportion to PCH₄ /(PH₂)², wherein PCH₄ is partial pressure ofmethane (CH₄), and PH₂ is partial pressure of hydrogen (H₂) in thereaction gas. In the case of a reducing reaction using hydrogen, as isapparent from formulas (1), (2), and (3), PH² /PH₂ O (wherein PH₂ O isthe partial pressure of steam) of the reaction gas is in proportion to areducing capability (i.e., chemical reaction force with respect toreduction). In the present invention, where the main component of thereaction gas is methane and hydrogen, and the concentration of methaneand hydrogen are adjusted to a proper proportion, and, further, steam(H₂ O) is maintained at a predetermined concentration or less, thereducing and carburizing reactions are allowed to proceed promptly andsimultaneously, thereby accomplishing a high reaction efficiency of thereaction gas. When the gas used in the second stage of the reactionprocess has the following composition:

    H.sub.2 +CH.sub.4 ≧65%(CH.sub.4 ≧20%), H.sub.2 O≦1.5%,

the gas meets the above conditions.

Then, CO or CO₂ acts as the reaction gas component of the carburizingreaction, and also as a catalyst in the carburizing reaction of methaneaccording to formula (10). As a result, the reaction speed is increased.Accordingly, it is preferable that CO or CO₂ is present in apredetermined concentration in order to shorten the reaction time. Afteridentical first stages of the reaction process were conducted using theexperimental apparatus of FIG. 1, second stages of the reaction processwere conducted by changing the percentage of CO+CO₂ in the inletreaction gas. The results are summarized in FIG. 11.

FIG. 11(a) illustrates a relationship between the average carburizingrate at a carburization ratio of 30 to 75% and inlet percentage ofCO+CO₂. As shown in FIG. 11(a), the average carburizing speed increasesas the inlet (CO+CO₂) percentage increases, and the average carburizingspeed is saturated at about 20%. For practical industrial applications,it is desired that the average carburizing speed is not less than6%/hour, and, therefore, it is important for the percentage of CO+CO₂ tobe at least about 0.3%. The average outlet-inlet (CO+CO₂) percentageduring the second stage of the reaction process, when the inlet (CO+CO₂)% of the second stage gas is changed, is shown in FIG. 11(b). As isapparent from FIG. 11(b), when the inlet (CO+CO₂) % is low, CO+CO₂ isproduced during the reaction between CO+CO₂ and material. When the inlet(CO+CO₂) % is high, CO+CO₂ is consumed. That is, when the inlet CO+CO₂is not less than about 3%, it is sometimes necessary that CO+CO₂ issupplied to the circulating gas.

It is an object of the present invention to use methane as the mainreaction component in the carburizing reaction to minimize the feed ofCO+H₂ by reforming natural gas as described above. Accordingly, bysatisfying the following formula:

    15%≧CO+CO.sub.2 ≧0.5%,

the industrially important effect of reaction speed (i.e., shortening ofreaction time) is obtained, and, at the same time, high carburizingreaction efficiency is achieved. Therefore, when the gas used forconducting the second stage of the reaction process has the compositionsatisfying the following formula:

    H.sub.2 +CH.sub.5 ≧65%(CH.sub.4 ≧20%),

    15%≧CO+CO.sub.2 ≧0.5%, H.sub.2 O<1.5%,

inert gas component such as N₂ ≦20%, the reaction time is shortened,thereby making it possible to use the method in practical industrialapplications.

6. According to the present method of producing iron carbide, theproportion of hydrogen gas can be changed by adding methane gas to thereducing gas of the first stage of the reaction process, therebyallowing control of the reaction speed of the reducing reaction.Therefore, it is possible to control the reduction degree in the firststage of the reaction process, control the reaction time to attain thepredetermined reduction degree, and, at the same time, control theamount of metallic iron in the product of the first stage of reactionprocess.

Also, it is possible to prevent deterioration of the reducing capabilityof the gas (i.e., decrease in CO and H₂ concentration, and increase inH₂ O concentration) by controlling the synthesis of methane from thereaction between carbon monoxide and hydrogen set forth in the followingformula (13). The reaction speed of the reducing reaction is maintained,thereby making it possible to control the reaction time and to decreasereaction gas consumption and the feed of hydrogen and carbon monoxide.

    CO+3H.sub.2 =CH.sub.4 +H.sub.2 O                           (13)

Furthermore, it is possible to change the composition ratio of hydrogento methane by adding hydrogen or methane to the reducing and carburizinggas in the second stage of the reaction process. Therefore, the reactionspeed of the carburizing reaction can be controlled. Accordingly, it ispossible to control the carburization ratio (i.e., conversion ratio intoiron carbide) and reaction time until a predetermined carburizationratio is obtained in the second stage of the reaction process.

A relative relationship between reaction speed of the remaining reducingreaction and that of the carburizing reaction can be controlled, therebymaking it possible to continue the reducing reaction shown in theformulas (1), (2), and (3), while conducting the carburizing reactionshown in the formula (4). In addition, the carburization ratio of thefinal product, as well as form and amount of the residual iron oxide,can be controlled, and, at the same time, the reaction time can beshortened and the most efficient use of reaction gas in a circulatingmanner can be accomplished.

7. According to the present process for producing iron carbide, if thereduction degree of hematite in the first stage of the reaction processis in the range of 50 to 65%, then, the total reaction time, as thetotal of the first and second stages of the reaction process, is theshortest, and, at the same time, the amount of hydrogen gas generated bythe carburizing reaction in the second stage of the reaction process andthe amount of hydrogen gas required for the reducing reaction are almostidentical. Therefore, the second stage of the reaction process can beperformed by supplying only the carburizing gas from a point of thechemical reaction balance.

Because the reaction speed of a catalytic reaction between a solid and agas normally is low, the gas is circulated, thereby taking effective useof the gas into consideration. That is, a component of the reaction gasis supplied to maintain a constant composition of the reaction gas,while circulating a fixed amount of the reaction gas. In the presentinvention, hydrogen and methane can be supplied in the first and secondstages of the reaction process, respectively.

8. According to the present method of producing iron carbide, the finalconversion ratio of hematite to iron carbide is in the range of 90 to 99atom %, and, therefore, a suitable product is obtained. When theconversion ratio is less than 90 atom %, the quality of the iron carbideis low. On the other hand, when the conversion ratio is greater than 99atom %, the amount of generated free carbon becomes large.

9. According to the present method of producing iron carbide, thereaction temperature of the first stage of the reaction process is inthe range of 550° to 750° C., and, therefore, a temperature suitable forperforming the above reaction is obtained. When the reaction temperatureis less than 550° C., the reaction speed is low and the reaction time islong. Therefore, it is necessary to adjust the temperature higher than550° C. On the other hand, when the reaction temperature is greater than750° C., it adversely affects the heat-resistant structure of thereactor. As described above, in the reducing reaction of hematite,sintering occurs in the range of about 600° to 700° C. resulting inincrease of the reaction time, and, therefore, the reaction is conductedat a temperature lower than the above temperature range, e.g., at about590° C. in the traditional method. In the present method of producingiron carbide, the reducing reaction is divided into two stages and thereduction degree in the first stage of the reaction process is notparticularly high. Therefore, even if the reaction temperature is high,no sintering occurs and adverse affects, such as a lower reaction speed,do not occur.

10. According to the present method of producing iron carbide, thereaction temperature of the second stage of the reaction process is inthe range of 550° to 750° C. Therefore, sintering or adhesion of thereacted iron ore to the furnace wall does not occur, which makes it easyto control the form (e.g., magnetite or wustite) of the residual ironoxide in the iron carbide product and to shorten the reaction time.

That is, in the second stage of the reaction process, remainingreduction, carburization, and conversion into iron are allowed toproceed simultaneously (since carburization proceeds when the reductionratio is high, sintering is less likely to occur than in the case whereonly reduction is conducted), and the reaction is conducted in the rangewhere the sintering or adhesion of iron ore to the furnace wall does notarise. Therefore, the reaction time is shortened when the reactiontemperature is increased. Accordingly, the second stage preferably isconducted in the range where sintering or adhesion of iron ore to thefurnace wall does not occur, e.g., 610° to 750° C.

In the second stage of the reaction process, it is also important notonly to achieve the desired conversion ratio into iron carbide (Fe₃ C),but also to control the chemical form (e.g., metallic iron (Fe),magnetite (Fe₃ O₄), wustite (FeO), etc.) of the residual iron in orderto obtain product stability against spontaneous combustion duringtransport and long-term storage of the product. The relative stabilityof iron compounds with respect to an exothermic reaction with water isin the order of Fe₃ O₄ (most stable), FeO, and Fe. At the time oflong-term transport and storage, it is sometimes desired to convert asmuch of the residual iron component as possible, i.e., the componentother than iron carbide (Fe₃ C) in the iron carbide product, to Fe₃ O₄,which is most stable. In that case, as is apparent from FIG. 9, FeO doesnot exist at about 575° C. or less, and, therefore, it is possible toconduct the reaction at a temperature of about 550° to 570° C., suchthat all the residual iron component is in the form of Fe₃ O₄.

11. According to the present method of producing iron carbide, thereaction temperature of the second stage of the reaction process is inthe range of 590° to 750° C., which is a suitable temperature forrapidly producing iron carbide. The reason is as follows. As shown inFIG. 9, the magnetite (Fe₃ O₄) region is broad at a reaction temperatureof 590° C. or less in the Fe--H--O system reduction equilibrium. Whenmagnetite is present in the reducing reaction for a long period of time,the final stage of the carburizing reaction to produce iron carbide isslowed down, and it takes a long time to fully convert to Fe₃ C.Therefore, it is necessary to adjust the reaction temperature to 590° C.or more, which is far from the magnetite zone, and the ratio of H₂ O to(H₂ O+H₂) can be set at comparatively high level. That is, the reductioncan be conducted to obtain as much metallic iron content as possibleusing the same ratio of H₂ O to (H₂ O+H₂) and the same amount of thereaction gas, and the higher carburizing reaction speed from themetallic iron-to-iron carbide can be maintained even at the final stageof the carburizing reaction into iron carbide because of existence ofmetallic iron. On the other hand, when the reaction temperature isadjusted to 750° C. or more, it adversely affects the heat-resistantstructure of the reactor. Further, carburization is conductedprogressively after reduction in the second stage of the reactionprocess, and, therefore, no sintering arises. Accordingly, the reactiontemperature can be increased.

12. According to the present method of producing iron carbide, steam isremoved from the reaction gas used in the second stage of the reactionprocess to decrease the partial pressure of steam. Therefore, theFeO--Fe zone can be widened and the magnetite zone can be narrowed inthe Fe--H--O system reduction equilibrium. Accordingly, it is possibleto prevent slowing down of the carburizing reaction because of thepresence of magnetite, thereby shortening the reaction time.

13. According to the present method of producing iron carbide, carbondioxide and hydrogen are added to the reaction gas in the second stageof the reaction process. Thereby, the following reaction formula (14)proceeds, and the concentration of carbon monoxide and carbon dioxideincreases. As the result, the carburizing reaction speed can besubstantially increased.

    CO.sub.2 +H.sub.2 →CO+H.sub.2 O                     (14)

14. According to the present method of producing iron carbide, thereaction pressures of the first and second stages of the reactionprocess are in a range of 1 to 9.9 kgf/cm² G. This reaction pressure issuitable to achieve the above reactions. When the reaction pressure isless than 1 kgf/cm² G, the reaction speed is low, and, therefore,reaction time is long. On the other hand, when the reaction pressure ismore than 9.9 kgf/cm² G, steam in the reactor is condensed and adheresto the feed raw materials. The feed then does not flow uniformly, whichresults in decrease of the conversion ratio into iron carbide. Inaddition, higher pressure badly affects the strength of the reactor andreactor gas supply tube.

With respect to the influence of pressure on the reducing reaction,which is mainly conducted in the first stage of the reaction process,and on reducing reaction speed, the reducing degree normally increasesas the pressure increases to 5 to 6 atm (i.e., above 4 to 5 kgf/cm² G).When the pressure is greater than the above range, the influence ofpressure on the reducing rate is small, and the pressure of 6 atm lessis economical for practical use.

In the second stage of the reaction process, the remaining reducing andcarburizing reactions are conducted. In order to maintain high reducingand carburizing reaction forces, even if the gas is used in acirculating manner, it is preferable that H₂ O generated in the reducingreaction is removed to reduce the H₂ O concentration as much aspossible. When the gas is subjected to a cooling treatment to remove H₂O, the amount of H₂ O can be relatively lowered when the pressure ishigh. As the pressure increases, the equilibrium concentration of themethane component of the carburizing reaction increases, and theconcentration of hydrogen as the reducing component becomes relativelylower. Therefore, it is preferable to operate under a sufficientpressure to maintain a proper relationship between the reducing rate andcarburizing rate. A preferable pressure is about 3 to 6 atm. Thisoperating pressure can be adjusted to a proper level, thereby making itpossible to shorten the reaction time and to achieve favorable reactioneconomics.

15. According to the present method of producing iron carbide, afine-sized raw material introduced into reactors of the first and secondstages of the reaction process are preheated or precooled to atemperature within ±100° C. of the reaction temperature of each phase.Therefore, the raw material feed does not agglomerate, and condensedsteam does not adversely affect the ability of the raw material to flow.Because the reducing reaction shown in above formulas (1) to (3) is anendothermic reaction, the feed is cooled. The feed supplied to thesecond stage of the reaction process has particularly high reactionactivity and generates steam rapidly at the beginning of the reaction tocool the feed, and, therefore, the generated steam is condensed toadhere to the feed, thereby inhibiting the flow of the feed.Accordingly, the feed supplied to the reactor is preheated to about thereaction temperature to prevent steam from condensing and to prevent adecrease in reaction speed.

Furthermore, the temperature of the first stage of the reaction processcan exert an influence on the reaction speed of the subsequent secondstage of the reaction process depending upon the form of theiron-bearing raw material for iron making. For example, the surface areaper unit weight of the raw material is increased by conducting thereduction of the first phase at a temperature which is several tens ofdegrees lower than that of the second reaction process. This supplies araw material to the second stage of the reaction process having a moreactive and partially metallized state. Then, the remaining reducing andcarburizing reactions of the raw material, which is reactively active,are performed, which results in a shortened total reaction time.

In order to maximize the amount of residual iron component of the ironcarbide product as stable magnetite, and also to shorten the totalreaction time, it also is possible to perform the second stage of thereaction process at a low temperature, such as 575° C. or less, afterthe first stage is conducted at a temperature as high as possible.

In accordance with the present invention, it is sometimes necessary toadd a sufficient heat to the raw material in the reactor of the firststage of the reaction process, and to charge a preheated raw materialfor the purpose of supplying a portion of the reaction heat, therebyavoiding excessive heating of the reaction gas. In addition topreheating the raw material charged in the first stage of the reactionprocess, it is sometimes necessary to perform a preliminary treatment,such as removal of combined water from the starting material. In thatcase, it is effective to conduct the preheating operation at atemperature which is at least 100° C. higher than the temperature of thefirst stage of the reaction process, as a matter of course. The presentinvention covers such an operation.

16. With respect to a present apparatus for producing iron carbide, oneembodiment thereof is set forth in FIG. 5. The first stage of thereaction process performs a reduction until 25 to 70 atom % of totaliron in the raw material is metallized, and the second stage of thereaction process performs the remaining reduction and conversion intoiron carbide (Fe₃ C). The reactions are respectively conducted inindependent reaction apparatus 41 and 61. The removal of dust from anexhaust gas after completion of the reactions and removal of an impuritygas component are conducted in scrubbers 45 and 65. Reaction gases,after being supplemented with a reduction gas or a carburization gas forthe control of the gas composition, are fed to reactors 41 and 61, viarecirculation compressors 42 and 62 and gas heater 43 and 63,first-stage gas circulation loop 40, and second-stage reaction gascirculation loop 60, making it possible to feed a reaction gas tofirst-stage reactor 41 and to second-stage reactor 61, independently.Furthermore, it is easy to adjust and control the respective optimumoperating conditions corresponding to the components and reactioncharacteristics of the raw material, and control components in the finalproduct. It is also possible to downsize the equipment and decreaseenergy consumption, thereby improving economy.

The above apparatus can serve as a batch-wise production apparatus or acontinuous production apparatus by supplying a raw material to a firstreaction apparatus 41 via a raw material supply line 80, and bytransferring a partially metallized raw material prepared in firstreaction apparatus 41 to a second reaction apparatus 61 via a transferline 81, and discharging an iron carbide product prepared in secondreaction apparatus 61 via a discharging line 82, either batch-wise orcontinuously. In case of a continuous production process, particularly,an Fe₃ C product having a high carburization ratio, or an Fe₃ C producthaving a slight variation in composition, can be efficiently producedusing a fluidized bed reaction apparatus, wherein an inner reaction zonecontains a partition wall to provide a route for the raw materialthrough the reaction apparatus.

Furthermore, in accordance with the embodiment illustrated in FIG. 16,when connecting lines 101 and 102 are provided between first-stage gascirculating loop 40 and second-stage gas circulating loop 60 to supply aportion of a gas containing a high concentration of hydrogen componentin first-stage gas circulating loop 40 to second-stage gas circulatingloop 60, or to supply a portion of a gas containing a high concentrationof methane in second-stage gas circulating loop 60 to first-stage gascirculating loop 40. Lines 101 and 102 make it possible to supply aparticular reaction gas component (e.g., hydrogen, methane, etc.) in anamount corresponding to the amount of the gas component is consumed,which in turn corresponds to the amount of reaction in the respectivereactors, and make it possible to efficiently control the concentrationof reaction gas components.

17. According to the present apparatus for producing iron carbide, bothfirst and second stages of the reaction process, respectively, areconducted in a fluidized bed reactor. A fluidized bed reactor optimizesa reaction which brings a solid iron-containing raw material for ironmaking into contact with a reducing and a carburizing gas for conversioninto iron carbide. A fluidized bed reactor uniformly conducts a reactionwherein a fine-sized iron-containing raw material is charged into anupper portion of the reactor, and a reaction gas is supplied from alower portion of the reactor. The supply and discharge of raw materialand product can be continuously performed. Furthermore, the reactiontime is shortened because of large contact area.

18. According to the present apparatus for producing iron carbide, areactor provided with partition walls for preventing direct movement ofraw material from the inlet to the outlet is used as the fluidized bedreactor. Such a reactor prevents the raw material and the reactionproduct from mixing in the reactor. Accordingly, the conversion ratiointo an Fe₃ C product can be increased. Normally, it is difficult forone fluidized bed reactor having no partition wall to increase thereaction degree, and, therefore, the reaction degree is increased byconnecting a plurality of reactors in series. In accordance with thepresent invention, it is possible to obtain a high reaction degree usingonly one fluidized bed reactor having partition walls.

It is possible to prevent a raw material (i.e., feed) at the inlet ofthe reactor and the product at the outlet from mixing, and, therefore,the reaction can be uniformly conducted.

19. According to the present apparatus for producing iron carbide, it ispossible to efficiently produce iron-containing raw materials for ironmaking, even if the raw material contains a large amount of coarseparticles having a diameter of greater than 6 mm. In the method of thepresent invention, the amount of reaction gas is comparatively large,and the reaction gas is sufficiently contacted with the solid particles.A fluidized bed reactor is suitable as the reaction apparatus for afine-sized raw material. In case of the raw materials containing a largeamount of coarse particles having a diameter of greater than 6 mm, forexample, a large amount of reaction gas is required for fluidizing. Inthis case, however, in a vertical moving bed reactor, it is necessary tohorizontally flow the gas in order to decrease a pressure loss and tobring a comparatively large amount of gas into contact with a new gas,uniformly, along the vertical direction. Accordingly, it is possible tosupply a reaction gas, uniformly, along the vertical direction bysupplying a reaction gas through inlet and outlet wind boxes locatedalong the corresponding heights of opposite rectangular reactor walls.

It is possible to conduct the first and second stages of the reactionprocess using one vertical moving bed reactor by connecting the upperinlet and outlet wind boxes to a supply duct for a reaction gas and toan exhaust gas duct for the first stage of the reaction process,respectively, and connecting the lower inlet and outlet wind boxes to asupply duct for a reaction gas and an exhaust gas duct for the secondstage of the reaction process. In this case, it is possible to preventthe first and second-stage reaction gases from mixing by adjusting thedistance between the lowermost stage wind box for the first reaction gasand the uppermost stage wind box for the second reaction gas to one totwo times as long as the length between walls in the horizontal gas flowdirection of the reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an experimental apparatus forpracticing the method of producing iron carbide according to oneembodiment of the present invention;

FIG. 2 is a graph plotting a relationship between the composition ratioof raw material (feed) and time from the results of experiment (A)carried out using the testing apparatus of FIG. 1;

FIG. 3 is a graph plotting a relationship between the composition ratioof raw material (feed) and time from the results of experiment (B)carried out using the testing apparatus of FIG. 1;

FIG. 4 is a graph plotting a relationship between the composition ratioof raw material (feed) and time from the results of experiment (C)carried out using the testing apparatus of FIG. 1;

FIG. 5 is a schematic diagram illustrating a production apparatus forpracticing the method for producing iron carbide according to oneembodiment of the present invention;

FIG. 6(a) is a longitudinal cross section illustrating a fluidized bedreactor which can be used in the production apparatus of FIG. 5, andFIG. 6(b) is a transverse cross section of the said reactor;

FIG. 7(a) and 7(e) are transverse cross sections illustrating variousembodiments of the fluidized bed reactor of FIG. 6;

FIG. 8 is a graph illustrating a relationship between the reactiontemperature (°C.) and reaction time (min) in the reducing reaction ofiron ore;

FIG. 9 is an equilibrium diagram of an Fe--H--O system;

FIG. 10 is a table illustrating a relationship between types ofcarburizing reaction gas and requisite amount of steam-gas reformation;

FIG. 11(a) is a graph illustrating a relationship between concentrationof carbon monoxide and carbon dioxide and carburizing speed, and FIG.11(b) is a graph illustrating an increase/decrease ratio of carbonmonoxide and carbon dioxide in the reaction gas;

FIG. 12 is a schematic illustrating a relationship between the reducingreaction and carburizing reaction in a process where iron carbide isproduced from iron oxide;

FIG. 13(a) is a graph illustrating a relationship between thecarburizing speed and ratio of metallic iron-to-iron oxide, and FIG.13(b) is a table illustrating examples of the apparent carburizingreaction speed with respect to each raw material;

FIG. 14(a) and (b) are graphs illustrating a relationship between themetallization degree and reaction time in the first stage of thereaction process;

FIG. 15(a) is a graph illustrating a relationship between circulatinggas flow rate and temperature/pressure, and FIG. 15(b) is a tableillustrating a composition of the product;

FIG. 16 is a schematic diagram illustrating another embodiment of anapparatus for producing iron carbide, which is used for practicing amethod for producing iron carbide according to one embodiment of thepresent invention;

FIG. 17 is a graph with respect to Table 1, illustrating a change inoutlet gas composition after reaction of the inlet gas composition;

FIG. 18 is a graph with respect to Table 2, illustrating a change inoutlet gas composition after reaction of the inlet gas composition;

FIG. 19 is a graph illustrating results of a test on the effect of gaspressure using a thermo-balance carburizing reaction experimentaldevice;

FIG. 20 is a schematic diagram illustrating one embodiment of a benchscale testing apparatus for testing various raw materials under variousoperating conditions, using the apparatus of FIG. 5;

FIG. 21 is a schematic diagram illustrating one embodiment of a verticalmoving bed reactor of the present invention, which is suitable forproducing iron carbide from a coarse grained raw material, wherein a gasflows horizontally and the solid raw material is charged and movesvertically through the reactor; and

FIG. 22(a) is a graph illustrating FIGS. 1, 5, 6, and 7 as results ofcold model tests which were carried out to confirm the effect ofpartition walls present in the interior of a fluidized bed reactor, andFIG. 22(b) is a table illustrating a conversion ratio of iron carbidewhich was derived from the results in the table.

DESCRIPTION OF THE INVENTION

Hereafter, experiments for practicing the method of producing ironcarbide in accordance with the present invention, and results thereof,are explained. Furthermore, embodiments of an apparatus for producingiron carbide in accordance with the present invention is explained,together with the production process.

1. Experimental Apparatus

One embodiment of an experimental apparatus for practicing a method ofproducing iron carbide of the present invention comprises a fluidizedbed reactor 1 and peripheral apparatus therefor, as shown in theschematic diagram of FIG. 1. Fluidized bed reactor 1 generally has acylindrical shape and is provided with a heating means 2, such as anelectric heater, to provide a predetermined temperature. In thisembodiment, a pipe having nominal diameter of 50 mm was used as theprincipal part of fluidized bed reactor 1. In addition,temperature-detecting sensors 3a, 3b, 3c, 3d, 3e, and 3f were positionedalong the length of fluidized bed reactor 1, at 127 mm, 187 mm, 442 mm,697 mm, and 1707 mm from the bottom of fluidized bed reactor 1, and atthe top of fluidized bed reactor 1, respectively, in order to measurethe temperature of the interior of reactor 1.

A hopper 5 was connected to the upper peripheral portion of fluidizedbed reactor 1 by a line 4 via a lock hopper 6 and a plurality of valves26 to permit flow of a fine-sized feed (e.g., hematite (Fe₂ O₃)), in apressurized state, from hopper 5 into fluidized-bed reactor 1. Inaddition, a cooler 8 was operatively connected to the bottom peripheralportion of fluidized bed reactor 1 via a line 7 to sufficiently coolmaterial discharged from the interior of reactor 1.

The bottom of fluidized bed reactor 1 was connected to a gas holder 10via lines 11 and 12 to allow flow of a reaction gas of predeterminedcomposition in gas holder 10 into fluidized bed reactor 1. Further, asaturator 13 is operatively positioned between lines 11, 12 to saturatethe reaction gas with water.

Lines 20, 21, and 22 were connected in series to one another, and line20 was connected to the upper peripheral portion of fluidized bedreactor 1 to direct an exhaust gas from the reaction to an incineratorapparatus (not shown). In addition, raw material dust contained in theexhaust gas can be removed using a dust collector 23 operativelypositioned between lines 20, 21 and a filter 27 inserted into line 21.Line 21 further was provided with a gas cooler 25 for cooling theexhaust gas to condense water, which is separated in a drain separator24 operatively positioned between lines 21 and 22.

2. Experimental Conditions and Results

A. First, a single operation, that is, a conventional process ofsubjecting an iron ore containing mainly hematite (i.e., Fe₂ O₃) to acatalytic reaction using a mixed gas containing a reducing gas and acarburizing gas to convert the iron ore into iron carbide (Fe₃ C) wasperformed. The experimental conditions were:

The iron ore used for the experiment had a composition of Fe (65.3% byweight), Al₂ O₃ (1.67% by weight), SiO₂ (3.02% by weight), and P (0.080%by weight). The iron ore (3.52 kg) was charged into fluidized bedreactor 1 after sizing into a particle size of not more than 1.0 mm(i.e., amount of the fine-sized iron ore having the particle size of 1.0to 0.1 mm was not less than 80% by weight and the particle size of notmore than 0.068 mm was 13.4% by weight). The composition of the reactiongas was as follows:

CO+CO₂ : about 5%, CO₂ +H₂ O≦about 4%, H₂ +CH₄ : about 85% (CH₄ >H₂), N₂≦about 8%.

Then, the reaction gas was allowed to flow into fluidized bed reactor 1at a flow rate of 2.15 Nm³ /hour. The temperature and pressure influidized bed reactor 1 were maintained 590° C. and 3 kgf/cm² G,respectively. The data using these experimental conditions oftemperature and pressure are summarized in detail in Table 1.

                                      TABLE 1                                     __________________________________________________________________________         Temperature (°C.)                                                 Time (hr.)                                                                         (from the bottom of reactor)                                                                             Pressure                                      Elapsed                                                                            127 mm                                                                            187 mm                                                                            442 mm                                                                            697 mm                                                                            1707 mm                                                                            Free Board                                                                          (kgf/cm.sup.2 G)                              __________________________________________________________________________    0.0  513 517 534 536 526  507   3.0                                           0.5  214 252 579 578 555  518   3.0                                           1.0  199 232 577 583 562  528   3.0                                           1.5  199 223 590 589 574  550   3.0                                           2.0  202 217 594 596 578  552   3.0                                           2.5  204 220 595 597 583  556   3.0                                           3.0  204 220 592 595 585  561   3.0                                           3.5  206 225 597 600 583  562   3.0                                           4.0  205 223 598 599 584  563   3.0                                           4.5  208 227 603 604 583  563                                                 5.0  205 223 599 599 583  564                                                 5.5  207 235 612 615 585  564                                                 6.0  199 220 607 608 582  565                                                 6.5  206 232 607 607 580  566                                                 7.0  205 233 609 609 580  566                                                 7.5  208 235 607 608 579  566   2.5                                           8.0  205 231 601 603 581  565                                                 8.5  312 578 595 595 582  564                                                 9.0  559 566 591 594 581  564   2.9                                           9.5  568 577 600 600 581  564   3.0                                           10.0 549 557 586 593 581  564   3.1                                           10.5 560 571 599 603 581  564                                                 11.0 559 569 598 600 580  564                                                 11.5 561 571 597 600 583  564                                                 12.0 560 570 599 600 583  565                                                 12.5 556 568 597 599 583  565                                                 13.0 564 575 605 603 583  566                                                 13.5 563 574 601 601 582  566                                                 14.0 551 563 583 587 580  566                                                 14.5 556 570 600 599 581  566                                                 15.0 557 568 601 601 581  567                                                 15.5 555 571 603 602 580  566                                                 16.0 547 562 597 598 578  566                                                 16.5 542 561 597 598 579  566                                                 17.0 215 262 608 610 579  564                                                 17.5 198 229 599 601 581  563                                                 18.0 205 228 592 593 579  561                                                 18.5 205 227 590 591 578  558                                                 19.0 207 230 589 591 578  556                                                 19.5 205 227 590 591 583  556                                                 20.0 204 227 590 592 584  556                                                 __________________________________________________________________________

Table 1 includes the temperature (temperature columns in Table 1) andpressure (pressure column in Table 1) which were measured every 30minutes after onset of the reaction. The columns headed 127 mm, 187 mm,442 mm, 697 mm, 1707 mm, and free board in the temperature columns arethe temperatures detected by temperature-detecting sensors 3a, 3b, 3c,3d, 3e, and 3f of FIG. 1, respectively. An outlet gas compositionresulting from a reaction utilizing the inlet gas composition is shownin FIG. 17. This gas composition was detected by a mass spectrometer,and inspected several times by gas chromatography.

The experimental results obtained under the above-described conditionsare shown in FIG. 2. The abscissa and ordinate of the graph plotted inFIG. 2 respectively set forth time (in hours) and an atomic ratio ofiron (for example, Fe₃ C: 90% means that 90% of the total iron atomsexist as Fe₃ C). It is apparent from FIG. 2 that about 20 hours arerequired for the conversion ratio to Fe₃ C to attain 93 atom %, which issufficient for an iron carbide product (Fe₃ C).

B. A method step of subjecting a raw material to a catalytic reactionusing a reducing gas (hereinafter referred to as a first stage of areaction process), and then a method step of subjecting the reactionproduct of the first stage to a catalytic reaction using a gas mixturecontaining reducing and carburizing gases (hereinafter referred to as asecond stage of the reaction process) were conducted in an experimentconverting iron ore into iron carbide. In other words, experiment wasdivided into a partial reducing reaction and the remaining reducing anda carburizing reaction in accordance with the present invention. Theexperimental conditions are described in detail hereafter.

The composition and amount of iron ore charged into fluidized bedreactor 1, the flow rate of the reaction gas, and the pressure influidized bed reactor 1 were identical to those of the above experiment(A), but the composition of the reaction gas and temperature influidized bed reactor 1 were varied. That is, the composition of thereaction gas of the first stage of the reaction process, which wasconducted for 3 hours from the onset of the reaction, was as follows:

H₂ : about 74%, N₂ : about 25%.

Three hours after beginning the first stage of the reaction process, thegas composition used in the second stage of the reaction process was asfollows:

CO+H₂ O: about 6%, CO₂ +H₂ O≦about 3.5% (H₂ O≦1.5%),

H₂ +CH₄ : 80 to 85% (CH₄ >H₂), N₂ ≦10%.

The temperature in fluidized bed reactor 1 was maintained at 600° C. Thedata obtained using these experimental conditions are summarized indetail in Table 2, which is similar to above-described Table 1.

                                      TABLE 2                                     __________________________________________________________________________         Temperature (°C.)                                                 Time (hr.)                                                                         (from the bottom of reactor)                                                                             Pressure                                      Elapsed                                                                            127 mm                                                                            187 mm                                                                            442 mm                                                                            697 mm                                                                            1707 mm                                                                            Free Board                                                                          (kgf/cm.sup.2 G)                              __________________________________________________________________________    0.0  581 583 593 604 590  602                                                 0.5  576 581 596 604 603  583                                                 1.0  583 590 601 607 608  576                                                 1.5  589 594 603 606 591  555                                                 2.0  592 599 604 608 602  571                                                 2.5  594 601 606 608 608  571                                                 3.0  587 592 605 609 614  568                                                 3.5  590 595 606 608 599  566                                                 4.0  591 598 607 610 599  559                                                 4.5  590 596 606 609 608  562                                                 5.0  590 598 607 609 601  560                                                 5.5  586 595 606 609 607  561                                                 6.0  591 597 606 610 599  564                                                 6.5  588 592 605 609 603  567                                                 7.0  589 596 605 610 597  568                                                 7.5  580 587 607 610 598  569                                                 8.0  589 596 607 610 587  563                                                 8.5  579 587 611 613 594  570                                                 __________________________________________________________________________

An outlet gas composition resulting from a reaction utilizing the inletgas composition is shown in FIG. 18. Hydrogen primarily was consumed inthe first stage of the reaction process, and methane primarily wasconsumed in the second stage of the reaction process to obtain theresults which are similar to formula (7) as the overall reactionformula.

The experimental results obtained using the above conditions aresummarized in FIG. 3 which is similar to FIG. 2. It is apparent from thegraph in FIG. 3 that about 7.5 hours are required for the conversionratio to Fe₃ C to reach 93 atom %, which is suitable for an iron carbideproduct (Fe₃ C), and the reaction time is substantially shortenedcompared to the above experiment (A). The reason is that the process isdivided into two stages, i.e., a portion of the reducing reaction ofiron ore in a first stage, and the remaining reducing reaction and acarburizing reaction in a second stage. Therefore, taking only thereducing reaction into consideration, the concentration of hydrogen canbe increased in the first stage of the reaction process. The reductionratio of the respective stages are not extremely large, and, therefore,no sintering arises and the reaction temperature can be increased toabout 600° C.

C. Finally, an experiment was conducted in the same manner as thatdescribed in above experiment (B), except for varying the reactiontemperature and pressure. The experimental conditions are explainedhereafter.

The composition and amount of iron ore charged into fluidized bedreactor 1, and the flow rate of the reaction gas were identical to aboveexperiment (B). The first stage of the reaction process was conductedfor 1.5 hours after the onset of the reaction using a reaction gashaving a composition as follows:

H₂ : about 70%, (N₂ +CH₄): about 30%.

One and one-half hours after beginning the reaction, the composition ofthe reaction gas for the second stage of the reaction process wasadjusted as follows:

CO+C₂ O: about 7%, CO₂ +H₂ O≦4.0% (H₂ O≦1.5%),

H₂ +CH₄ : 80 to 85%, N₂ ≦10%.

The temperature and pressure in fluidized bed reactor 1 were maintainedat 650° C. and 5 atm, respectively.

The experimental results obtained under the above conditions are plottedin FIG. 4, which is similar to FIGS. 2 and 3. It is apparent from FIG. 4that about 5.5 hours were required for the conversion ratio to Fe₃ C toreach 93 atom %, which is suitable for an iron carbide product (Fe₃ C),and that the reaction time can be substantially shortened compared tothe above experiment (A), and is similar to the above experiment (B).The generation rate of iron carbide did not decrease at the latter partof the reaction because the reaction temperature was increased.

EMBODIMENT 3. An Apparatus for Producing Iron Carbide

A large-scale apparatus capable of performing a continuous conversion isrequired in order to economically produce an iron-containing material,which contains iron carbide as a main component, for iron making inblast furnaces, cupolas, etc., and for steel making in converters,electric furnaces, etc. One embodiment of an apparatus for producingiron carbide according to the present invention is set forth in theschematic diagram of FIG. 5.

As shown in FIG. 5, the apparatus of this embodiment comprises afirst-stage reaction process portion, referred to as a first-stage gascirculating loop 40, for conducting a partial reducing reaction of aniron ore containing mainly hematite as the iron-containing raw materialfor iron making and a second-stage reaction process portion, referred toas a second-stage gas circulating loop 60, for conducting the remainingreducing reaction and a carburizing reaction. With respect to flowthrough first-stage circulating loop 40, lines 46 and 47, compressor 42,line 48, heat exchanger 44, line 49, heater 43, line 50, fluidized bedreactor 41, line 51, heat exchanger 44, line 52, scrubber 45, and line53 form first loop 40. That is, a reaction gas is introduced near thebottom of fluidized bed reactor 41, such as through a gas inlet, vialine 47, compressor 42, line 48, heat exchanger 44, line 49, heater 43,and line 50 in order. The reaction gas exits from near the top offluidized bed reactor 41 through line 51, heat exchanger 44, line 52,scrubber 45, line 53, line 46, and line 47 to form a loop forcirculating the first reaction gas. The reaction gas flowing from thebottom to the top of fluidized bed reactor 41 is circulated bycompressor 42. Gas flowing into fluidized bed reactor 41 is subjected toheat exchange in heat exchanger 44 with gas flowing from reactor 41after the completion of the reaction, and then is heated by gas heater43. Scrubber 45 comprises a hollow body 58, a line 56 for spraying wateronto the gas, and a line 57 for discharging water from body 58. Gasflowing from reactor 41 is cooled, and steam present in the gas iscondensed for removal. Furthermore, a gas having a predeterminedcomposition can be supplied to loop 40 through a line 54 connected at aconjunction between lines 46 and 47, and a predetermined amount of gascan be withdrawn from loop 40 through a line 55 connected at aconjunction between lines 53 and 46. The feed gas and discharge gas areadjusted to maintain a constant composition of reaction gas flowing intofluidized bed reactor 41, thereby preventing a change in gas compositionand a decrease in reaction speed.

In addition, the flow of a second reaction gas through second-stage gascirculating loop 60 is identical to the flow of the first reaction gasthrough loop 40 as shown in FIG. 5, wherein reference numbers for secondloop 60 are obtained by adding 20 to the reference number ofcorresponding elements in first loop 40. An explanation of the elements,and their function, of second loop 60 is set forth above with respect tofirst loop 40.

Regarding the flow of raw material feed in the reactor, a fine-sizediron ore is continuously supplied to the upper portion of fluidized bedreactor 41 of first-stage gas circulating loop 40 via a charging routecomprising line 80, and the raw material feed which has already beensubjected to a partial reducing reaction in reactor 41 is allowed toflow continuously from the bottom portion of fluidized bed reactor 41 tofluidized bed reactor 61 of second-stage gas circulating loop 60 via asupply route comprising a line 81. The remaining reducing reaction andthe carburization reaction are performed in fluidized bed reactor 61 andthe converted iron carbide is continuously discharged through arecovering route comprising a line 82.

Regarding the gas composition used in the respective first and secondstages, the first stage of the reaction process is performed using areducing gas containing mainly hydrogen because only the reducingoperation is occurring. The concentration of hydrogen is high toincrease the reaction speed of the reducing reaction, thereby making itpossible to shorten the reaction time in comparison with a conventionalmethod. The second stage of the reaction process is performed using agas mixture containing hydrogen and methane because both reducing andcarburizing reactions are occurring. However, the reducing reaction waspartially performed in the first stage of the reaction process, and,therefore, the carburizing reaction can be considered as more important.Accordingly, the concentration of methane gas can be increased in orderto increase the reaction speed of the carburizing reaction, therebymaking it possible to shorten the reaction time. A predetermined amountof methane gas can be added to the reducing gas containing mainlyhydrogen of the first stage of the reaction process to decrease theconcentration of hydrogen, thereby making it possible to control thespeed of the reduction reaction. On the other hand, the speed of thecarburization reaction can be controlled by adjusting the concentrationof methane in the second stage of the reaction process, thereby makingit possible to control reaction time with little generation of freecarbon and a predetermined desired carburization ratio.

In the apparatus for producing iron carbide of this embodiment, thereduction degree of hematite in the first stage of the reaction processwas in the range of 50% to 65 atom % of total iron atoms. Thereby, theamount of hydrogen required for the reducing reaction in the secondreaction is identical to the amount generated in the carburizingreaction. Therefore, only methane gas can be supplied as the reactiongas of the second stage of the reaction process. The reason is that, asis apparent from the above formulas (1) to (4), a ratio of hydrogenrequired for the reducing reaction to that generated in the carburizingreaction is 9:4 when the iron (Fe) content is constant. Therefore, it ispossible to meet the demand and supply of hydrogen gas in the secondstage of the reaction process by respectively adjusting the reductiondegree in the first and second stages of the reaction process to about56 atom % and the remaining 44 atom %, stoichiometrically. The gascomposition used when the apparatus is operated under the aboveconditions is set forth in Table 3.

                                      TABLE 3                                     __________________________________________________________________________           1st Stage. 4 ATM 590° C.                                                               2nd Stage, 4 ATM 590° C.                               Make-up                                                                            Reactor                                                                           Reactor                                                                           Bleed                                                                            Make-up                                                                            Reactor                                                                           Reactor                                                                           Bleed                                            Gas  Inlet                                                                             Outlet                                                                            Gas                                                                              Gas  Inlet                                                                             Outlet                                                                            Gas                                       __________________________________________________________________________    % CO + CO.sub.2                                                                      0.20 2.06                                                                              2.11                                                                              2.68                                                                             0.47 2.88                                                                              2.84                                                                              3.01                                      % CO.sub.2 + H.sub.2                                                                 1.60 2.03                                                                              23.16                                                                             2.17                                                                             1.23 1.68                                                                              7.14                                                                              1.70                                      % H.sub.2 + CH.sub.4                                                                 97.80                                                                              94.60                                                                             73.45                                                                             93.51                                                                            97.63                                                                              94.79                                                                             89.41                                                                             94.64                                     % N.sub.2                                                                            0.50 2.48                                                                              2.48                                                                              3.14                                                                             0.95 1.64                                                                              1.58                                                                              1.68                                      NCM/T* 411  1618                                                                              1619                                                                              61 200  3786                                                                              3916                                                                              103                                       __________________________________________________________________________

The columns headed first and second stages in Table 3, respectively,indicate the first and second stages of the reaction process. Thecolumns subheaded make-up gas, bleed gas, reactor inlet, and reactoroutlet, respectively, indicate the composition of a gas supplied fromlines 54 and 74 of FIG. 5 to first and second circulating loops 40 and60, the composition of a gas removed through lines 55 and 75, thecomposition of a gas flowing into reactors 41 and 61, and thecomposition of a gas flowing out from reactors 41 and 61. The headingNCM/T* indicates the flow rate, in Nm³ /t, wherein N means a volume innormal state, of the reaction gas required per ton (weight in dry state)of raw material to be reacted. Further, the pressure and temperature inreactors 41 and 61 were respectively adjusted to 4 atm and 590° C. Asdescribed above, only hydrogen is consumed in the first stage of thereaction process and the amount of methane gas barely changes, and,therefore, only a reducing reaction proceeds. On the other hand, onlymethane gas is consumed in the second stage of the reaction process andthe amount of the hydrogen gas does not change, and, therefore, hydrogengenerated in the carburizing reaction is balanced by the hydrogenconsumed in the reducing reaction. In order to increase the reactionspeed of the carburizing reaction, and to shorten reaction time, theapparatus was operated by changing the reaction temperature and pressureof the first and second stages of the reaction process to 650° C. and 5atm. The results are summarized in Table 4, which is similar to Table 3.The flow rate of the circulating gas in these two embodiments issubstantially decreased in comparison to a conventional apparatus.

                                      TABLE 4                                     __________________________________________________________________________           1st Stage. 5 ATM 650° C.                                                               2nd Stage, 5 ATM 650° C.                               Make-up                                                                            Reactor                                                                           Reactor                                                                           Bleed                                                                            Make-up                                                                            Reactor                                                                           Reactor                                                                           Bleed                                            Gas  Inlet                                                                             Outlet                                                                            Gas                                                                              Gas  Inlet                                                                             Outlet                                                                            Gas                                       __________________________________________________________________________    % CO + CO.sub.2                                                                      0.30 1.96                                                                              1.93                                                                              2.27                                                                             2.59 6.59                                                                              6.35                                                                              6.77                                      % CO.sub.2 + H.sub.2                                                                 0.20 1.58                                                                              16.50                                                                             1.83                                                                             3.49 2.91                                                                              9.07                                                                              2.87                                      % H.sub.2 + CH.sub.4                                                                 99.05                                                                              90.96                                                                             76.05                                                                             89.42                                                                            94.52                                                                              86.77                                                                             80.90                                                                             86.41                                     % N.sub.2                                                                            0.49 6.19                                                                              6.20                                                                              7.29                                                                             1.99 5.61                                                                              5.42                                                                              5.79                                      NCM/T* 366  2278                                                                              2277                                                                              19 156  3433                                                                              3556                                                                              45                                        __________________________________________________________________________

The energy consumed preparing an iron-carbide product having an Fe₃ Cconversion ratio of 90 atom % or greater is produced by an apparatushaving a production scale of 500,000 tons per year, and using naturalgas, is calculated based on the above results. The calculations aretabulated in Table 8b. The amount of energy consumed in a conventionalprocess for producing direct reduced iron or iron carbide is describedin publication 10 and is tabulated in Table 8a. It has been found that asimilar or remarkably improved result is obtained by the presentinvention.

                                      TABLES 8a-8b                                __________________________________________________________________________    Table 8a                                                                                                        Prior art of                                                                          Table 8b                                                              IRON CARBIDE                                                                          The Present                         Process   WIDREX                                                                              HYL III                                                                           FIOR                                                                              AREX  FIORII                                                                            Process Invention                           __________________________________________________________________________    Pressure  Atmospheric                                                                         5 bars                                                                            10 bars                                                                           Atmospheric                                                                         10 bars     3-6 bars                            Typical Plant Capacity                                                                   1     1  0.4 0.5    1  0.32    0.5                                 (mmt/y*)                                                                      Energy Input                                                                            2.5   2.7 4.0           3.0     2.7                                 (Gcal/Wt)                                                                     Natural Gas (G/mt)                                                                       10   10.9                                                                               18 8.7    13  13     11.5                                Elect. (kWh/mt)                                                                         125   85  200 70    150 230     130                                 Product Metallization                                                                   >92%  >92%                                                                              93% 93%   93% Fe.sub.a C > 90%                                                                      Fe.sub.a C > 90%                    Product Carbon Con-                                                                     1-2%  1-4%                                                                              0.5%                                                                               2%   1.5%                                                                              <6% (Fe.sub.a C)                                                                      <6% (Fe.sub.a C)                    tent                                                                          __________________________________________________________________________     *mmt/y = million metric tons per year                                         Table 8a From publication 10                                                  Table 8b Process example for industrial plant (scale 500,000 tons/year)       according to the present invention and calculated from the above test         results                                                                  

4. Method for Producing Iron Carbide

(a) The conversion ratio from hematite to iron carbide is in the rangeof 90 to 99 atom %, preferably 93 atom % or more, and more preferably 95atom % or more. The higher the conversion ratio, the greater the valueof the Fe₃ C product.

(b) The reaction temperature of the first stage of the reaction processis in the range of 550° to 750° C., preferably 600° to 750° C. Asdescribed above, the reduction degree is not carried to a high value inthe first stage of the reaction process of the present invention, and,therefore, sintering does not arise and it is possible to operate at600° C. or more. Accordingly, the reaction temperature preferably israised to increase the reaction speed.

(c) The reaction temperature of the second stage of the reaction processis in the range of 550° to 750° C., preferably 590° to 750° C. As soonas the reducing reaction is completed in the second stage of thereaction process, the carburizing reaction then proceeds. Therefore, nosintering occurs at a reaction temperature of 600° to 700° C., and thecarburizing reaction can be performed. Accordingly, the reactiontemperature preferably is increased to increase the reaction speed ofreduction and carburization. Furthermore, as shown in FIG. 9, when thereaction temperature is increased to 590° C. or more, the region wheremagnetite (Fe₃ O₄) exists becomes narrow and region where FeO existsbecomes wide in the Fe--H--O system reduction equilibrium. The presenceof magnetite decreases the speed of conversion into iron carbide at thefinal stage of the carburizing reaction. Therefore, the reaction time isshortened by narrowing the region where magnetite exists.

(d) The reaction pressure in the first and second stages of the reactionprocess is in the range of 1 to 9.9 kgf/cm² G, preferably 2 to 5 kgf/cm²G. When the pressure in fluidized bed reactors 41 and 61 is too low, itis difficult to fluidize the feed iron ore, and, therefore, the diameterof reactors 41 and 61 must be enlarged. The reaction speed also isreduced. On the other hand, when the reaction pressure is too high, itadversely affects the pressure-resistant strength of the body ofreactors 41 and 61 and attendant valves, piping, etc.

(e) Fluidized bed reactors 41 and 61 shown in FIG. 5 are illustrated asa single reactor for simplifying the explanation. However, the reactionof the present invention is a catalytic reaction between a solid andgas, and the reaction degree is low. Therefore, in accordance with thepresent invention, a plurality of fluidized bed reactors 41 and 61 canbe connected in series to carry out the reactions. Since the reactionspeed of the respective reactions is high, the reaction can besufficiently conducted using 1 to 4 reactors.

(f) The amount of steam in the reaction gas, which is rapidly generatedat the beginning of the first stage of the reaction process, is reducedby condensing steam from the circulating gas with cooling (by scrubber45 of FIG. 5) or by bleeding out a determined amount of steam per unittime. By reducing the amount of steam, the disadvantages of feedagglomeration due to condensation of steam, and failure of the feed tofluidize uniformly, can be prevented. Further, steam can be removed moreefficiently by cooling the circulating gas to 10° to 25° C.

(g) Steam generated in the reaction gas in the second stage of thereaction process also is decreased by condensing water from thecirculating gas with cooling (by scrubber 65 of FIG. 5). Reduction ofthe amount of steam in the reaction gas of the second stage of thereaction process has an advantageous effect described hereafter.

That is, as the partial pressure of steam in the reaction gas is reducedby removing steam, the Fe--H--O system equilibrium in the reducingreaction (see FIG. 9) shows that the partial pressure of hydrogenincreases. Therefore, the region where magnetite exists, which causes areduction in the speed of conversion to iron carbide as described above,becomes narrow, while the region where Fe and FeO exist becomes wide,which leads to shortened reaction time. It is particularly preferablethat the concentration of steam in the gas used for conducting thesecond stage of the reaction process is decreased to a range that can becontrolled industrially. Accordingly, the concentration of H₂ Opreferably is adjusted to not more than 1.5%.

On the other hand, when no steam is present in a gas used in the secondstage of the reaction process, free carbon is generated according to thefollowing reactions.

    CH.sub.4 →C+2H.sub.2                                (15)

    CO+H.sub.2 →C+H.sub.2 O                             (16)

Therefore, when the pressure is increased, or the amount of steam isincreased, the generation of free carbon due to the reactions offormulas (15) and (16) can be reduced. Accordingly, the concentration ofsteam has a lower limit, and the concentration of H₂ O is adjusted tonot less than 0.2% in a normal operation. When free carbon is generated,steam can be added to prevent the generation of free carbon.

(h) In the first stage of the reaction process, for example, CO₂ gas isremoved using a CO₂ scrubber (e.g., by utilizing a gas absorptionprocess with solvent), which results in a decreased concentration of COand CO₂ which are in a chemical equilibrium relation. The decrease in COand CO₂ concentration decreases the concentration of methane in achemical equilibrium relation to prevent generation of free carbon, andfurther relatively increases the concentration of hydrogen gas toincrease the reaction speed of the reduction.

(i) In the first and second stages of the reaction process, the rawmaterial feed supplied to fluidized bed reactors 41 and 61 is preheatedto a temperature ±100° C. of the reaction temperature. Therefore,agglomeration of the feed due to condensation of steam generated at thebeginning of the reducing reaction, and failure to fluidize the feed,can be prevented. Since the reducing reaction is an endothermicreaction, steam has a tendency to condense. Because the reducingreaction in the second stage of the reaction process proceeds rapidly,such a disadvantage is particularly likely to occur. In addition to apreheating operation, a gas having a temperature which is decreased fromthe predetermined temperature by 10° to 100° C. can be used for thereaction at the beginning of the second stage of the reaction process inorder to decrease the reaction speed, thereby making it possible toprevent generation of free carbon deposits and condensation of steam.

(j) The degree of the progress of the reducing reaction in the firststage of the reaction process, i.e., the reduction degree, can bedetermined by measuring the amount of steam present in the circulatinggas. If the reduction degree can be determined, a variation in reactiontime caused by variation in quality of the iron ore can be easilycontrolled.

(k) The reaction speed of the reducing reaction is controlled by addinga predetermined amount of methane to the make-up gas containing mainlyhydrogen in the first stage of the reaction process. On the other hand,the reaction speed of the carburizing reaction can be controlled byadding a predetermined amount of hydrogen to the make-up gas containingmainly methane in the second stage of the reaction process. Therefore,the carburizing reaction having a high carbon activity can be controlledto prevent free carbon generation.

Further, the flow rate of methane and hydrogen, which are consumed inthe first and second stages of the reaction process, isstoichiometrically determined by the amount of iron ore to be treated(referred to as ideal amount). Accordingly, as described above, theamount of methane added to the first stage of the reaction processpreferably is subtracted from the ideal amount of methane required forthe second stage of the reaction process, and the amount of hydrogenadded in the second stage of reaction process preferably is subtractedfrom the ideal amount of hydrogen required for the first stage of thereaction process.

(l) A bleed gas exhausted from lines 55 and 75 in the first and secondstages reaction process preferably is directed to an H₂ gas generatingunit to recycle H₂ gas.

(m) When using heaters 43 and 63 shown in FIG. 5 as a combuster, thegenerated exhaust gases are utilized for preheating the feed for aneffective use of energy.

(n) In the second stage of the reaction process, CO₂ +H₂ can be added.Thereby, the concentration of CO and CO₂ in the circulating gas of thesecond phase of the reaction process preferably is increased by about 30to 50%. The presence of CO and CO₂ can substantially increase thereaction speed of the carburizing reaction to achieve a substantialdecrease in reaction time.

(o) The temperature of the raw material feed supplied to the reactors 41and 61 is increased to a temperature higher than the preheatingtemperature described in the above item (i) (e.g., 50° to 150° C. abovethe said preheating temperature). On the other hand, the temperature ofthe circulating gas introduced into reactors 41 and 61 is decreased. Thereactions can be performed when conducting such an operation. Inaddition, when such an operation is performed, damage to lines, such aslines 50 and 70 for the circulating gas, caused by the generation offree carbon or carburization of steel can be decreased.

(p) It is necessary to cool the iron carbide produced by the first andsecond stages of the reaction process because reaction activity of Fe₃ Cis high at elevated temperatures. The iron carbide preferably is cooledrapidly to a temperature at which the reaction activity is low, such asby admixing with iron carbide which previously had been cooled toambient temperate, followed by cooling the resulting mixture to ambienttemperature. According to this process, iron carbide can be cooledreadily.

In addition, rapid cooling of iron carbide preferably is conducted in acooled process gas or an atmosphere of an inert gas, such as N₂, orunder pressurized conditions. Thereby, conversion of iron carbide toother compounds is prevented.

In the apparatus shown in FIG. 5, when the partial reduction, ormetallization %, in the first stage of the reaction process, e.g., valueof x of FeO_(x), shifts to a value different from, i.e., larger orsmaller than, 2/3 according to the formula (11), i.e., relation ofFeO_(2/3) shown in Table 5, an excess or a lack of a reducing gascomponent, particularly hydrogen, arises in second phase gas circulatingloop 60, while methane is synthesized according to the formula (13) infirst phase gas circulating loop 40, which results in disadvantages,such as a decrease in reduction reaction speed due to accumulation ofmethane.

                  TABLE 5                                                         ______________________________________                                        Example of FeO.sub.2/3 Composition                                                                  Coexistence                                                                   of metal iron                                                                 with wustite                                                                  and magnetite                                                                 A ratio of                                                                    the number of                                                                 iron atoms in                                                                 Wustite to Coexistence                                            Coexistence those in Mag-                                                                            of metal                                     Construction                                                                            of metal iron                                                                             netite is  iron with                                    example   with wustite                                                                              50:50      magnetite                                    ______________________________________                                        Metal iron                                                                              34          43         51                                           atoms (atom                                                                   %)                                                                            Iron atoms                                                                              66          57         49                                           as iron               (Fe in FeO:                                             oxide (atom           28.5 atom %                                             %)                    Fe in Fe.sub.3 O.sub.4 :                                                      28.5 atom %)                                            Reduction 56          56         56                                           ratio in                                                                      case of us-                                                                   ing hematite                                                                  as starting                                                                   material (%)                                                                  Metalliza-                                                                              34          43         51                                           tion degree                                                                   (%)                                                                           ______________________________________                                    

To overcome such disadvantage, as shown in FIG. 16, auxiliary lines 101,102, 103, and 104 are provided to connect circulating loops 40 and 60for the respective reaction gases and to connect supply lines 54 and 74of the gas components in the apparatus of FIG. 5. Auxiliary lines 101,102, 103, and 104 transfer a reaction gas in an auxiliary manner,thereby utilizing the circulating gas efficiently and adjusting andcontrolling the components in a reaction gas. Hereafter, one embodimentof the present method of producing iron carbide is summarized in Table7, with reference to FIG. 16.

                  TABLE 7                                                         ______________________________________                                        Embodiment of material for iron making and proper                             metallization degree of the first-stage reaction process                                     Material E for iron                                                                        Material G for iron                               Raw Materials  making       making                                            ______________________________________                                        Composition                                                                           T-Fe       66.0%        66.5%                                         of material                                                                           Fe.sub.2 O.sub.3                                                                         91.6%        93.8%                                                 Fe.sub.3 O.sub.4                                                                          2.8%         1.4%                                                 Gangue content                                                                            4.8%         3.6%                                                 L.O.I       0.8%         1.2%                                         Metallization ratio of the first-stage reaction process for                   shortening the whole reaction process time and composition                    ↓                                                                      X*              0.543 (<2/3)                                                                               0.836 (>2/3)                                     Metallization  55.7%        31.4%                                             degree                                                                        T-Fe           81.4%        77.2%                                             M-Fe           45.4%        24.2%                                             FeO            14.4%        23.8%                                             Fe.sub.3 O.sub.4                                                                             34.3%        47.8%                                             Gangue content  5.8%         4.1%                                             ______________________________________                                         *X means the numeric of x in FeO.sub.x                                   

The embodiment summarized in Table 7 shows the results obtained bysubjecting various iron-containing raw materials for iron making to atest wherein the degree of partial reduction in the first stage of thereaction process was changed in accordance with the process operationsshown in FIG. 3 and using the apparatus shown in FIG. 1, followed byanalysis as shown in FIG. 14. That is, it was assumed that a propermetallization degree in the first stage of the reaction process forminimizing total reaction time in case of the raw material E for ironmaking was 55.7 atom %, and x of corresponding FeO_(x) was about 0.543.In this case, x was 0.543, which is smaller than 2/3. When using methane(CH₄) as the main carburizing reaction gas component, hydrogen must besupplied to the reaction gas in addition to methane because of lack ofhydrogen for reduction. The amount of hydrogen supplied is about 40 to80 Nm³ per ton of iron carbide product. Two processes can be used as theprocess for supplying hydrogen, e.g., a direct supply from reducing gassupply line 54 via auxiliary line 103 shown in FIG. 16, and supply fromfirst circulating loop 40 containing a large amount of hydrogen viaauxiliary line 101. In first loop 40, the accumulation of methane due tothe reaction according to the above formula (13) occasionally arises,and, therefore, bleeding can be conducted via line 55. In this case, itis more effective to transfer the gas of first loop 40 to second loop60, which also requires supplying methane, via auxiliary line 101,thereby solving the problem efficiently.

In case of the raw material G for iron making shown in Table 7, theproper metallization ratio is low, such as 31.5 atom %, and x of thecorresponding FeO_(x) is high, such as 0.836, which is larger than 2/3.In this case, to the contrary to the above case, the concentration ofhydrogen in the gas in second circulating loop 60 increases in order.This means that the amount of bleed via line 75 must be increased. Inorder to effectively utilize hydrogen, a proper amount of hydrogen canbe transferred from second circulating loop 60 to first circulating loop40 via auxiliary line 102 to decrease the amount of bleed via line 75.In the case of raw material G for iron making, it is necessary to drawabout 160 Nm³ /one ton of product from second circulating loop 60, butit is most economical to transfer the gas of about 95 Nm³ /one ton ofproduct to first circulating loop 40 via auxiliary line 102, followed bybleeding the remaining gas of about 65 Nm³ /one ton of product via line57 to use as a fuel for gas heater 63.

5. Results of Tests Using Various Raw Materials and Operation Conditions

A bench scale test apparatus for testing various raw materials andoperation conditions was made using the apparatus of the embodimentshown in FIG. 5, and then a specific experimental operation wasconducted. The results are shown below.

The bench scale testing apparatus for testing has the construction setforth in FIG. 20 and comprises a first fluidized bed reactor 1 having aninner diameter of 200 mm and a second fluidized bed reactor having aninner diameter of 250 mm, and wherein each reactor is provided with onepartition wall for controlling the flow of iron ore in the respectivereactor.

First reactor 1 is provided with a circulating gas loop comprising a gascompressor 60, a gas preheater 62, first reactor 1, a dust collector 52,a gas-quenching device 54, and a gas holder 56.

After the gas reacted with the raw material in first reactor 1, fineparticles in the gas are removed by dust collector 52, the gas is cooledby gas-quenching device 54 and water as the reaction product is removed,and then the gas is introduced into gas holder 56.

Thereafter, gas consumed in the reducing reaction (i.e., mainlyhydrogen) is supplied from a supply gas line 59, and the excess gas isexhausted from the loop via a bleed gas line 57. Then, after adjustingto a predetermined pressure and temperature, gas is introduced intofirst reactor 1 using gas compressor 60 and gas heater 62.

Second reactor 2 also is provided with an identical gas circulatingloop, but the supply gas cylinder contains a different gas because thegas consumed in the second reaction system is different.

In addition, the raw material is heated and pressurized in a heated rawmaterial hopper 14, and then continuously introduced into first reactor1 using a heated raw material feeder 15. The raw material then iscontinuously transferred to second reactor 2 using a high-temperatureraw material transferring device 17. The product discharged from thesecond reactor 2 is stored in a high-temperature product storagecontainer 19.

The reducing gas and the methane for carburization are supplied, apartfrom the industrial equipment, by admixing the respective gases, whichare stored in high pressure cylinders, and a heat exchanger iseliminated. The operation was conducted continuously for 15 to 20 hoursat the flow rate of 45 to 200 Nm³ /hour of gas in the first stage of thereaction process and flow rate of 60 to 300 Nm³ /hour of gas in thesecond stage of the reaction process, at a temperature of 550° to 750°C., and under a pressure of 2 to 7 atmospheres, to obtain a sufficientlystable state.

Further, the reference symbols in FIG. 20 identify the followingelements:

1: First fluidized bed reactor (inner diameter: 200 mm, bed height: 5 m)

2: Second fluidized bed reactor (inner diameter: 250 mm, bed height: 7m)

3, 4: Insulating refractory provided with auxiliary electric heater forfirst and second reactors

11: Raw material supply inlet

12: Raw material heating apparatus provided with a paddle

13, 16: Seal valve

14: Heated raw material hopper

15: Heated raw material feeder

17: High-temperature raw material transferring apparatus (pneumaticconveying type)

18: Seal valve

19: High-temperature product storage container

31: Hydrogen gas cylinder

33: CO gas cylinder

35: CO₂ gas cylinder

37: CH₄ gas cylinder

39: CH₄ gas cylinder

32, 34, 36: Flow control valve

38, 40, 41: Flow control valve

42: Hydrogen gas connecting tube

51, 71: First and second reactor outlet gas ducts

52, 72: First and second reactor outlet dust collector

53, 73: First and second reactor gas duct after removing dust

54, 74: First and second reactor gas-quenching device

55, 75: First and second reactor quench gas ducts

56, 76: First and second reactor gas holders

57, 77: First and second reactor bleed gas ducts

58, 78: First and second reactor circulating gas ducts

59, 79: First and second reactor auxiliary gas supply ducts

60, 80: First and second reactor circulating gas compressors

61, 81: First and second reactor compressor outlet gas ducts

62, 82: First and second reactor gas preheaters

63, 83: First and second reactor inlet gas ducts

64, 84: First and second reactor partition walls

FIG. 15 summarizes the results of an experiment with respect to theinfluence of various temperatures and pressures, when using the samehematite iron ore that was used in the experiments of FIGS. 2, 3, and 4and using the apparatus of FIG. 20.

With respect to the effect of the temperature, as shown in FIG. 15, whenreaction temperature is increased, the reaction time not only isshortened, but also the amount of the reaction gas is decreased. Theresidual iron content in the iron carbide product is converted intomagnetite (Fe₃ O₄), which is stable to moisture in air, by adjusting thereaction temperature to about 575° C.

With respect to the effect of the pressure, as is apparent from therelationship of experiment Nos. 5, 6, and 7 summarized in FIG. 15, theamount of reaction gas decreases as the pressure changes in the order of7 atmosphere, 3 atmosphere, and 5 atmosphere. Accordingly, the maximumeffect can be exhibited at a pressure of about 3 to 6 atmosphere.

On the other hand, the rate of the carburizing reaction in the secondphase of the reaction process was measured at various gas compositionsand pressures at 600° C., under the conditions of the present invention,by using a small high temperature and high pressure thermo-balance-typereaction experimental device. The results are summarized in FIG. 19. Asis apparent from the results in FIG. 19, a shortened reaction time wasobtained due to increase in pressure. However, the effect of pressurebegins to decrease at about 6 to 7 atmosphere.

The results of tests on various iron ores and recycled materials foriron making generated in iron works, and using the apparatus of FIG. 20,are summarized in Table 6. The operating conditions of the tests are setforth in Table 4, that is, the pressure was 5 atmosphere and thetemperature was 650° C. The components of the reaction gases werecontrolled in the range of the components of the first and second stageinlet gases as set forth in Table 4.

                                      TABLE 6                                     __________________________________________________________________________    Results of production of iron carbide with                                    respect to various iron-containing materials for iron making                             Sample No.                                                                    No. 1                                                                              2   3    4    5    6                                                              Limonite       Dust gen-                                                      ore (con-                                                                          Mill      erated                                                         taining                                                                            scale                                                                              Dust gen-                                                                          from di-                                                       iron generated                                                                          erated                                                                             rect iron-                                            Hematite                                                                           Magne-                                                                            hydrox-                                                                            from iron                                                                          from making                                     Kind       ore  tite ore                                                                          ide) works                                                                              converter                                                                          furnace                                    __________________________________________________________________________    Composition                                                                         T.Fe 66.24%                                                                             66.79%                                                                            58.9%                                                                              72.61%                                                                             77.7%                                                                              76.0%                                      of material                                                                         Fe.sub.2 O.sub.3                                                                   94.9%                                                                              1.56%                                                                             2.1% --   40.4%                                                                              47.5%                                      (dry base                                                                           FeOOH                                                                              --   --  91.5%                                                                              --   --   --                                         percentage)                                                                         Fe.sub.3 O.sub.4                                                                   --   90.91%                                                                            --   84.03%                                                                             --   --                                               FeO  --   --  --   12.93%                                                                             15.3%                                                                              15.7%                                            M-Fe --   --  --   1.75%                                                                              37.6%                                                                              30.6%                                            Gangue                                                                             5.1% 7.53%                                                                             6.4% 1.29%                                                                              6.7% 6.2%                                             L.0.I                                                                              --   --  --   --   --   --                                         Product of                                                                          Metalli-                                                                           46.2%                                                                              54.9%                                                                             47.1%                                                                              51.1%                                                                              52.0%                                                                              50.9%                                      the   zation                                                                  first stage                                                                         (%)                                                                     reaction                                                                            X(FeO.sub.x)                                                                       0.731                                                                              0.755                                                                             0.692                                                                              0.678                                                                              0.661                                                                              0.664                                      process                                                                             M-Fe 36.25%                                                                             43.37%                                                                            36.31%                                                                             42.9%                                                                              41.27%                                                                             40.80%                                           Fe.sub.2 O.sub.3                                                                   5.95%                                                                              --  3.94%                                                                              --   2.55%                                                                              2.63%                                            Fe.sub.3 O.sub.4                                                                   37.45%                                                                             30.03%                                                                            35.69%                                                                             37.1%                                                                              39.02%                                                                             28.91%                                           FeO  14.28%                                                                             17.71%                                                                            15.74%                                                                             18.5%                                                                              10.20%                                                                             21.07%                                           Reaction                                                                           1.5 h                                                                              1.8 h                                                                             1.3 h                                                                              1.6 h                                                                              0.8 h                                                                              1.0 h                                            time                                                                    Product of                                                                          Ratio of                                                                           91.2%                                                                              91.9%                                                                             93.7%                                                                              88.1%                                                                              90.4%                                                                              93.2%                                      the second                                                                          conver-                                                                 stage sion into                                                               reaction                                                                            iron                                                                    process                                                                             carbide                                                                       Fe.sub.3 0                                                                         82.77%                                                                             80.90%                                                                            84.10%                                                                             84.17%                                                                             81.95%                                                                             85.20%                                           Fe.sub.2 O.sub.3                                                                   2.61%                                                                              --  1.93%                                                                              --   1.23%                                                                              1.53%                                            Fe.sub.3 O.sub.4                                                                   2.62%                                                                              4.91%                                                                             1.78%                                                                              7.84%                                                                              5.93%                                                                              3.29%                                            FeO  4.78%                                                                              4.57%                                                                             2.97%                                                                              5.78%                                                                              3.29%                                                                              2.32%                                            M-Fe 0.66%                                                                              0.36%                                                                             0.28%                                                                              0.62%                                                                              0.32%                                                                              0.68%                                            Gangue                                                                             6.54%                                                                              9.25%                                                                             8.93%                                                                              1.59%                                                                              7.28%                                                                              6.97%                                            Reaction                                                                           4.9 h                                                                              5.3 h                                                                             5.2 h                                                                              5.5 h                                                                              5.4 h                                                                              5.1 h                                            time                                                                    __________________________________________________________________________

As is apparent from the results summarized in Table 6, 1 to 3% ofunreacted hematite (Fe₂ O₃) is contained in the product, even though thereaction time is slightly increased in comparison with the results shownin FIG. 4, and, at the same time, the carburization ratio is lower thanthe results in FIG. 4. It is theorized that the reason for such a resultis that, although a partition wall is provided in the interior of thefluidized bed reactors of the first and the second stages to control theflow of iron ore and to prevent unreacted raw materials from mixing withreacted raw materials, only one partition wall is present because thediameter of the fluidized bed reactor is small, and also the width ofthe flow line in the fluidized bed reactor is narrow in comparison withthe bed height, making the ratio of fluidized bed height to diameterlarge. Therefore, the fluidizing state is unstable, which leads tomixing of raw material and product, and in addition, the flow of rawmaterial in the bed could not be controlled sufficiently, resulting inthe inclusion of 1 to 3% of hematite in the final Fe₃ C product. Anindustrial reactor provided with a partition wall, as shown in FIG. 6 orFIG. 7, solves the problem because the diameter of the reactor issufficiently large and a stable fluidizing state can be obtained.

6. Fluidized Bed Reactor

Improvements in the fluidized bed reactors are explained below. As isshown in FIGS. 6(a) and 6(b), partition walls 94 for preventing a directmovement of reactor feed from an inlet 92 to an outlet 93 were providedin the interior of a cylindrical side wall 90 and on the upper surfaceof a distribution plate 91. Accordingly, it takes a sufficiently longtime for the reactor feed to pass through the fluidized bed reactor,and, therefore, the reaction degree is high. A plurality of fluidizedbed reactors normally are connected in series in order to increase thereaction degree, but the requisite number of the reactors is reduced byusing a fluidized bed reactor of the present invention. By the use of apresent fluidized bed reactor, it is possible to prevent unreacted feedand reacted feed from admixing, and, therefore, the reactor feed isuniformly reacted. Further, a fluidized bed reactor of the presentinvention is not limited to the embodiment shown in FIG. 6, and can beof any design which provides a long flow distance from reactor inlet 92to outlet 93. Other embodiments are illustrated in FIGS. 7(a) through7(e). Of these embodiments, the reactors of FIGS. 7(d) and 7(e) have nodead zone where a swirl or a stagnation of material arises in the flowline of the feed into the reactor, thereby making it possible to performa more uniform reaction.

The results of a cold model test performed to confirm the effects ofpartition walls present in the interior of the fluidized bed reactor,and iron carbide conversion ratio of the product calculated from theresults, are shown in FIG. 22.

When no partition wall is provided, 40% of the total raw materialparticles introduced to the reactor were discharged within half (i.e.,0.5 θ) of the average residence time θ (amount of total particlesresiding in reactor/amount of particles introduced or discharged perunit time). In addition, 63% and 77% of the raw material, respectively,was discharged within θ and 1.5 θ. On the other hand, when the interiorof the same fluidized bed reactor is partitioned to contain fourcompartments, or when a linear partition is provided in the interior ofthe reactor, the discharge amount within 0.5 θ was 3% and 14%,respectively.

As is apparent from the above test results, when using a fluidized bedreactor having no partition wall, the residence time of the particles inthe reactor is short, and amount of particles discharged without beingconverted to iron carbide becomes large. Therefore, the expected ironcarbide conversion ratio when using a particular iron-containing rawmaterial for iron making is about 66%.

To the contrary, when the interior of the same fluidized bed reactor ispartitioned in an identical manner as that of the above tests, theamount of particles discharged in a small period of time decreases.Therefore, the expected iron carbide conversion ratio, when using thesame iron-containing raw material for iron making, is improved to about90%, if the reactor is partitioned into four compartments. If a linearpartition is provided, the conversion ratio is improved to about 84%.

7. Vertical Moving Bed Reactor

FIG. 21 is a schematic diagram illustrating a vertical moving bedreactor of the present invention, wherein a gas suitable for producingiron carbide from a coarse grain raw material flows horizontally and thecharged raw material flows vertically.

As illustrated in FIG. 21, in this embodiment, a vertical moving bedreactor 6 has a first reaction zone 300 and a second reaction zone 400to form a single vertical moving bed reactor.

In first reaction zone 300, a gas inlet 30 for the gas of the firststage of the reaction process provides gas to an inlet wind box 23 vialines 31 and 33 through an inlet header 22 to flow into the moving bed,almost horizontally, and then is discharged as an outlet gas through anoutlet 35 for the first stage of the reaction process via an outlet windbox 24 and an outlet header 25 through lines 32 and 34.

Also, in second reaction zone 400, a gas inlet 40 for the second stageof the reaction process is discharged as an outlet gas through outlet 47for the second stage of the reaction process via lines 41, 43, 45, 42,44, and 46.

The feed raw material is pressurized via elements 1 through 5 prior tointroduction to first reaction zone 300. The reduction is conducted infirst reaction zone 300 and the remaining reduction and a carburizationis conducted in second reaction zone 400, and then the product isdepressurized via elements 7 through 11 and discharged semicontinuously.

Each reference symbol in FIG. 21 denotes the following elements.

1: Raw material feed hopper

2, 4: Gas seal valves

3: Raw material intermediate hopper

5: Raw material feed hopper with control device

6: Rectangular vertical moving bed reactor

7: Product outlet

8: Product discharge apparatus with control device

9, 11: Gas seal valves

10: Discharge intermediate hopper

22: Reaction gas inlet header for the first-stage reaction process

23: Reaction gas inlet wind box for the first-stage reaction process

24: Reaction gas outlet wind box for the first-stage reaction process

25: Reaction gas outlet header for the first-stage reaction process

30: Inlet reaction gas for the first stage reaction process

31, 33: Reaction gas inlet ducts for the first-stage reaction process

32, 34: Reaction gas outlet ducts for the first-stage reaction process

35: Outlet reaction gas for the first-stage reaction process

40: Inlet reaction gas for the second-stage reaction process

41, 43, 45: Reaction gas inlet ducts for the second stage reactionprocess

42, 44, 46: Reaction gas outlet ducts for the second-stage reactionprocess

47: Outlet reaction gas for the second-stage reaction process

52: Reaction gas inlet header for the second-stage reaction process

53: Reaction gas inlet wind box for the second-stage reaction process

54: Reaction gas outlet wind box for the second-stage reaction process

55: Reaction gas outlet header for the second-stage reaction process

EFFECT OF THE INVENTION

As is apparent from the above, a method and apparatus for producing ironcarbide in accordance with the present invention has the followingadvantages.

1. According to the present method of producing iron carbide, thereaction time can be shortened. The reaction can be conducted at a hightemperature without causing sintering, and, therefore, the reactionspeed can be further increased and reaction time can be shortened. Anapparatus having the same scale as an apparatus practicing aconventional method, therefore, exhibits increased production capacity.

The flow rate of the reducing and carburizing gases which are requiredfor the first and second stages of the reaction process can besubstantially reduced because of an increase in reaction temperature, ashortening of the reaction time, etc. Therefore, even though the flow ofreaction gas requires two systems and the apparatus is complex, themethod provides sufficient economies because of a decrease in the flowrate of the reaction gas and an increase in production, etc.

Furthermore, because various adjustments can be employed in eachreaction phase, which cannot be employed in a conventional method forproducing iron carbide, such as the single process described in thepublication of Japanese translation of International Patent ApplicationNo. 6-501983 (PCT/US91/05198), the present method is a flexible process,thereby making it easy to control process parameters, such as theconversion ratio and reaction speed.

2. According to the present method of producing iron carbide, advantagesdescribed in above item 1 can be exhibited by using a gas which isreadily available.

The amount of the reforming gas for producing hydrogen and carbonmonoxide can be decreased in comparison with a conventional processwhich uses a gas-containing carbon monoxide (CO) as the main componentof the carburizing reaction, as described in publications 6 and 7. Inaddition, energy consumption is decreased and the process equipment canbe made small.

Furthermore, the reaction time of the first stage can be substantiallyshortened in comparison with a conventional process disclosed in GermanPatent No. 4320359, which comprises adding a portion of the carburizingreaction gas to the outlet reaction gas of the second stage, and usingthe resulting gas in the first-stage reaction, thereby making itpossible to achieve economics due to downsizing of the equipment.

3. According to the present method of producing iron carbide, even incases of reacting an iron-containing raw material other than hematite,e.g., other iron oxides, or iron hydroxides, or mixtures with metalliciron including dust and scale from iron works, it is possible to conductthe first stage of the reaction process to reduce the raw material to adetermined reduction degree/metallic iron content, irrespective of thestate of the iron oxides contained in the iron-containing raw materialor the state of the iron in the mixture of metallic iron, which issuitable for feeding to the second stage of the reaction process. As aresult, methane can be used as a suitable gas component of the mainreducing and carburizing reactions in the second stage of the reactionprocess. Therefore, it is possible to operate flexibly, while shorteningthe reaction time and decreasing the amount of reaction gas.

When the iron carbide product is used as the iron raw material in aniron-making or steel-making furnace, it is possible to supply a Fe₃ Cproduct having a predetermined property to perform a requisite function,such as the function of supplying a source of iron and energy, or thefunction of accelerating a refining action due to CO₂ generated byreacting oxygen of the residual oxide with carbon of iron carbide, whileexhibiting the advantages described in the above items (1) and (2) inaccordance with the process requirements of the respective furnace.

Furthermore, by adjusting the metallization degree in the first stage ofthe reaction process in the range of 25 to 70 atom %, methane can beadded exclusively to the second stage of the reaction process, and thetotal reaction time can be shortened. By adjusting the metallizationdegree within the range of 30 to 65 atom %, the total reaction time canbe minimized. By adjusting the final conversion ratio from saidiron-containing raw material for iron-making into iron carbide to atleast 75 atom %, the raw material for iron making or steel making havingan optimum conversion ratio can be produced.

4. According to the present method of producing iron carbide of theadvantages described in the above item (1) can be exhibited by using gascompositions which are readily available.

5. According to the present method of producing iron carbide, thereaction speed of the reducing reaction can be controlled, and,therefore, it is possible to control the reduction degree and thereaction time required to obtain a predetermined reduction degree in thefirst stage of the reaction process.

The reaction speed of the carburizing reaction can be controlled, and,therefore, it is possible to control the carburization ratio (i.e.,conversion ratio into iron carbide), and the reaction time required forobtaining a predetermined carburization ratio in the second stage of thereaction process. Therefore, it is possible to precisely control thereaction to a predetermined carburization ratio, while preventing freecarbon generation.

6. According to the present method of producing iron carbide, the amountof the hydrogen gas generated from methane during the carburizingreaction in the second stage of the reaction process, and the amount ofhydrogen required for the reducing reaction can be adjusted to beessentially identical, and, therefore, the second stage of the reactionprocess can be conducted merely by supplying a carburizing gas in viewof chemical reaction balance. Therefore, it is not necessary to performa complicated adjustment of the composition of the reaction gas. Even ifa circulating reaction gas is used, the hydrogen and methane gases canbe respectively supplied in the first and second stages of the reactionprocess, and, therefore, an operation, such as an adjustment of thecomposition of the reaction gas, is easy.

7. According to the present method of producing iron carbide, a suitableproduction state, which maintains the value of the iron carbide productand prevents generation of free carbon, is attained.

8. According to the present method of producing iron carbide, atemperature of the reaction can be selected which is suitable forexhibiting the above advantages while increasing reaction speed withoutadversely affecting the heat-resistant structure of the reactors.

9. According to the present method of producing iron carbide,disadvantages, such as sintering, generation of free carbon, etc., donot arise, and a shortened reaction time can be attained by increasingthe reaction operation temperature, as shown in FIGS. 3 and 4. The formof the residual iron in the iron carbide product can be magnetite (Fe₂O₄), which is stable to moisture in air, by setting the reactiontemperature at about 575° C. or less, as shown in FIG. 15. Therefore,the present method demonstrates a flexibility in reaction parameters.

10. According to the present method of producing iron carbide, thereaction temperature is suitable such that a slowdown in the conversionto iron carbide is prevented, a shortening of the reaction time isrealized, and an economy in equipment is realized.

11. According to the present method of producing iron carbide, theregion where FeO and Fe exist in the Fe--H--O system reductionequilibrium is wide, and the region where magnetite exists can benarrowed. Therefore, a slowdown in the carburizing reaction due to thepresence of magnetite is suppressed, and the reaction time is shortened.

12. According to the present method of producing iron carbide, theconcentration of carbon monoxide and carbon dioxide in the reaction gascan be increased. As a result, the reaction speed of the carburizingreaction can be increased substantially, as shown in FIG. 11.

13. According to the present method of producing iron carbide, apressure which is suitable for achieving the above advantages whileshortening the reaction time and satisfying the economy is possible.

14. According to the present method of producing iron carbide, it ispossible to prevent the raw material from agglomerating and failing toflow due to condensation of steam generated at the beginning of thereaction. Therefore, disadvantages, such as decrease in reaction speed,reaction degree, etc., are prevented.

15. The present method can be carried out using the present apparatusfor producing iron carbide. In an industrial scale apparatus, reactiontime is shortened and energy consumption is decreased, and the equipmentis made small in comparison to the apparatus used in a conventionalmethod, as shown in the right-end column of FIG. 8a.

16. According to the present apparatus for producing iron carbide, thereaction is optimized by bringing the solid iron-bearing raw materialfor iron making into contact with the reducing and carburizing gases forconversion into iron carbide.

17. According to the present apparatus for producing iron carbide, thereaction speed can be increased. Therefore, the number of the fluidizedbed reactors required to increase reaction speed can be decreased.

It also is possible to prevent the raw material at the inlet portion andthe Fe₃ C product at the outlet portion of the reactor from mixing, and,therefore, the reaction can proceed uniformly. Furthermore, a producthaving high iron carbide conversion ratio can be obtained in a reactionhaving the same average residence time.

18. According to the present apparatus for producing iron carbide, ahigh utilization efficiency of the reaction gas and a high iron carbideconversion ratio can be realized despite using a raw material comprisingmainly coarse particles, which typically is not suitable for fluidizing,and practical use of equipment can be accomplished.

What is claimed is:
 1. A method of producing iron carbide from aniron-containing material comprising hematite which comprises:providing afirst distinct apparatus and a second distinct apparatus, each apparatushaving an independent circulating loop of reaction gas, the reaction gasbeing distinct for each loop; passing the iron-containing materialcomprising hematite to said first distinct apparatus; contacting saidiron-containing material in said first distinct apparatus with saidindependent circulating loop of reaction gas to partially reduce saidiron-containing material to have a reduction degree of about 50% to 65%;passing said partially reduced iron-containing material to said seconddistinct apparatus; and contacting the partially reduced iron-containingmaterial in said distinct apparatus with an independent circulating loopof reaction gas to reduce and carburize said iron-containing material.2. The method of claim 1 wherein the reaction gas in said first distinctapparatus comprises hydrogen as a predominant component, and thereaction gas in the second distinct apparatus is a reducing andcarburizing gas comprising hydrogen and methane as predominantcomponents.
 3. The method of claim 1 wherein the temperature in saidfirst distinct apparatus and said second distinct apparatus is 590° to750° C.
 4. The method of claim 1 wherein the partial reduction in saidfirst distinct apparatus and the reduction and carburization reaction insaid second distinct apparatus are performed at a reaction pressure of 1to 9.9 kgf/cm² G.
 5. A method of producing iron carbide, the methodcomprising:providing a first distinct apparatus and a second distinctapparatus, each apparatus having an independent circulating loop ofreaction gas, the reaction gas being distinct for each loop; passing aniron-containing material to said first distinct apparatus; contactingsaid iron-containing material in said-first distinct apparatus with saidindependent circulating loop of reaction gas to produce a partiallyreduced iron-containing material having a metallic iron content of 25 to75 atom %; passing said partially reduced iron-containing material tosaid second distinct apparatus; and contacting said partially reducediron-containing material with an independent loop of reaction gas untilthere is a conversion ratio of partially reduced iron-containingmaterial to iron carbide of more than about 75 atom %.
 6. The method ofclaim 5 wherein the iron-containing material is selected from the groupconsisting of an iron ore, a material generated in an iron-makingprocess, an iron oxide, an iron hydroxide, and mixtures thereof.
 7. Themethod of claim 5 wherein the iron-containing material is selected fromthe group consisting of hematite, magnetite, wustite, ferrous hydroxide,ferric hydroxide, and mixtures thereof.
 8. The method of claim 5 whereinthe iron-containing material comprises hematite.
 9. The method of claim5 wherein the reacting gas in said first distinct apparatus is incapableof forming iron carbide and has a composition:H₂ +H₂ O≧40%, CO+CO₂ ≦10%,CH₄ ≦30%, H₂ O+CO₂ ≦10%, N₂ and the other inert gas components ≦25%. 10.The method of claim 5 wherein the reaction gas in said second distinctapparatus has a composition:H2+CH₄ ≧65% (CH₄ ≧20%), 15%≧CO+CO₂ ≧0.5%, H₂O≦1.5%, N₂ and the other inert gas component <20%.
 11. The method ofclaim 5 wherein methane is added to the reaction gas in said firstdistinct apparatus, and hydrogen or methane is added to the reaction gasin said second distinct apparatus.
 12. The method of claim 5 wherein theiron-containing material is partially reduced in said first distinctapparatus in an amount of 50 to 65%.
 13. The method of claim 5 whereinthe conversion ratio of the iron-containing material to iron carbide is90 to 99 atom % of total iron content.
 14. The method of claim 5 whereinthe reaction in said first distinct apparatus is performed at atemperature of 550° to 750° C.
 15. The method of claim 5 wherein thereaction in said second distinct apparatus is performed at a temperatureof 550° to 750° C.
 16. The method of claim 15 wherein the temperature is590° to 750° C.
 17. The method of claim, 7 wherein a partial pressure ofsteam in the reaction gas in said first distinct apparatus is decreasedby removing water vapor from said reaction gas.
 18. The method of claim5 wherein carbon dioxide and hydrogen are added to the reaction gas insaid second distinct apparatus.
 19. The method of claim 5 wherein thereactions in said first distinct apparatus and said second distinctapparatus are performed at a reaction pressure of 1 to 9.9 kgf/cm² G.20. The method of claim 5 wherein the iron-containing material ispreheated or precooled to a temperature within ±100° C. of reactiontemperature prior to performing the partial reduction reaction in saidfirst distinct apparatus, and prior to performing the reduction andcarburization reaction in said second distinct apparatus.